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PubMed1992

Regional changes in muscle mass following 17 weeks of bed rest.

This work reports on the muscle loss and recovery after 17 wk of continuous bed rest and 8 wk of reambulation in eight normal male volunteers. Muscle changes were assessed by urinary levels of 3-methylhistidine (3-MeH), nitrogen balance, dual-photon absorptiometry (DPA), magnetic resonance imaging (MRI), and isokinetic muscle performance. The total body lean tissue loss during bed rest calculated from nitrogen balance was 3.9 +/- 2.1 (SD) kg (P < 0.05). Although the total loss is minimal, DPA scans showed that nearly all of the lean tissue loss occurred in the lower limbs. Similarly, MRI muscle volume measurements showed greater percent loss in the limbs relative to the back muscles. MRI, DPA, and nitrogen balance suggest that muscle atrophy continued throughout bed rest with rapid recovery after reambulation. Isokinetic muscle strength decreased significantly (P < 0.05) in the thigh and calf with no loss in the arms and with rapid recovery during reambulation. We conclude that there is great variability in the degree and location of muscle loss in bed rest and that the lower limb muscles are primarily affected.

Absorptiometry, Photon↗
PubMed1998

Sympathetic discharge and vascular resistance after bed rest.

The effect of -6 degrees head-down-tilt bed rest (HDBR) for 14 days on supine sympathetic discharge and cardiovascular hemodynamics at rest was assessed. Mean arterial pressure, heart rate (n = 25), muscle sympathetic nerve activity (MSNA; n = 16) burst frequency, and forearm blood flow (n = 14) were measured, and forearm vascular resistance (FVR) was calculated. Stroke distance, our index of stroke volume, was derived from measurements of aortic mean blood velocity (Doppler) and R-R interval (n = 7). With these data, an index of total peripheral resistance was determined. Heart rate at rest was greater in the post (71 +/- 2 beats/min)- compared with the pre-HDBR test (66 +/- 2 beats/min; P < 0.003), but mean arterial pressure was unchanged. Aortic stroke distance during post-HDBR (15.5 +/- 1.1 cm/beat) was reduced from pre-HDBR levels (20.0 +/- 1.5 cm/beat) (P < 0.03). Also, MSNA burst frequency was reduced in the post (16.7 +/- 2.8 beats/min)- compared with the pre (25.2 +/- 2.6 beats/min)-HDBR condition (P < 0.01). Bed rest did not alter forearm blood flow, FVR, or total peripheral resistance. Thus reductions in MSNA with HDBR were not associated with a decrease in FVR.

Adaptation, Physiological↗
PubMed1998

Effects of posture on cardiovascular responses to lower body positive pressure at rest and during dynamic exercise.

We tested the hypothesis that cardiovascular responses to lower body positive pressure (LBPP) would be dependent on the posture of the subject and also on the background condition (rest or exercise). We measured heart rate (HR), mean arterial blood pressure (MAP), and cardiac stroke volume in eight subjects at rest and during cycle ergometer exercise (76 +/- 3 W) with and without LBPP (25, 50, and 75 mmHg) in the supine and upright positions. At rest, the increase in MAP was proportional to the increase in LBPP and was greater in the supine (6 +/- 2, 15 +/- 3, and 26 +/- 3 mmHg) than in the upright (2 +/- 3, 9 +/- 3, and 17 +/- 3 mmHg) position. During dynamic exercise, the increases in MAP evoked by 25, 50, and 75 mmHg LBPP were greater in the supine (13 +/- 2, 28 +/- 3, and 40 +/- 3 mmHg) than in the upright (7 +/- 3, 12 +/- 3, and 25 +/- 3 mmHg) position. We conclude that the systemic pressure response to LBPP is clearly dependent on the body position, with the larger pressure responses being associated with the supine position both at rest and during dynamic leg exercise.

Adult↗
PubMed2001

Energetic driving forces are maintained in resting rat skeletal muscle after dietary creatine supplementation.

The total creatine (TCr) pool of skeletal muscle is composed of creatine (Cr) and phosphocreatine (PCr). In resting skeletal muscle, the ratio of PCr to TCr (PCr/TCr; PCr energy charge) is approximately 0.6-0.8, depending on the fiber type. PCr/TCr is linked to the cellular free energy of ATP hydrolysis by the Cr kinase equilibrium. Dietary Cr supplementation increases TCr in skeletal muscle. However, many previous studies have reported data indicating that PCr/TCr falls after supplementation, which would suggest that Cr supplementation alters the resting energetic state of myocytes. This study investigated the effect of Cr supplementation on the energy phosphates of resting skeletal muscle. Male rats were fed either rodent chow (control) or chow supplemented with 2% (wt/wt) Cr. After 2 wk on the diet, the gastrocnemius and soleus muscles were freeze clamped and removed from anesthetized animals. Cr supplementation increased TCr, PCr, and Cr levels in the gastrocnemius by 20, 22, and 17%, respectively (P < 0.05). A numerical 6% higher mean soleus TCr in Cr-supplemented rats was not statistically significant. All other energy phosphate concentrations, free energy of ATP hydrolysis, and PCr/TCr were not different between the two groups in either muscle. We conclude that Cr supplementation simply increased TCr in fast-twitch rat skeletal muscle but did not otherwise alter resting cellular energetic state.

Animals↗
PubMed2003

Effects of 14 days of head-down tilt bed rest on cutaneous vasoconstrictor responses in humans.

This study tested the hypothesis that head-down tilt bed rest (HDBR) reduces adrenergic and nonadrenergic cutaneous vasoconstrictor responsiveness. Additionally, an exercise countermeasure group was included to identify whether exercise during bed rest might counteract any vasoconstrictor deficits that arose during HDBR. Twenty-two subjects underwent 14 days of strict 6 degrees HDBR. Eight of these 22 subjects did not exercise during HDBR, while 14 of these subjects exercised on a supine cycle ergometer for 90 min a day at 75% of pre-bed rest heart rate maximum. To assess alpha-adrenergic vasoconstrictor responsiveness, intradermal microdialysis was used to locally administer norepinephrine (NE), while forearm skin blood flow (SkBF; laser-Doppler flowmetry) was monitored over microdialysis membranes. Nonlinear regression modeling was used to identify the effective drug concentration that caused 50% of the cutaneous vasoconstrictor response (EC(50)) and minimum values from the SkBF-NE dose-response curves. In addition, the effects of HDBR on nonadrenergic cutaneous vasoconstriction were assessed via the venoarteriolar response of the forearm and leg. HDBR did not alter EC(50) or the magnitude of cutaneous vasoconstriction to exogenous NE administration regardless of whether the subjects exercised during HDBR. Moreover, HDBR did not alter the forearm venoarteriolar response in either the control or exercise groups during HDBR. However, HDBR significantly reduced the magnitude of cutaneous vasoconstriction due to the venoarteriolar response in the leg, and this response was similarly reduced in the exercise group. These data suggest that HDBR does not alter cutaneous vasoconstrictor responses to exogenous NE administration, whereas cutaneous vasoconstriction of the leg due to the venoarteriolar response is reduced after HDBR. It remains unclear whether attenuated venoarteriolar responses in the lower limbs contribute to reduced orthostatic tolerance after bed rest and spaceflight.

Adult↗
PubMed2003

Effects of chronic heart failure on skeletal muscle capillary hemodynamics at rest and during contractions.

Chronic heart failure (CHF) reduces muscle blood flow at rest and during exercise and impairs muscle function. Using intravital microscopy techniques, we tested the hypothesis that the speed and amplitude of the capillary red blood cell (RBC) velocity (VRBC) and flux (FRBC) response to contractions would be reduced in CHF compared with control (C) spinotrapezius muscle. The proportion of capillaries supporting continuous RBC flow was less (P < 0.05) in CHF (0.66 +/- 0.04) compared with C (0.84 +/- 0.01) muscle at rest and was not significantly altered with contractions. At rest, VRBC (C, 270 +/- 62; CHF, 179 +/- 14 microm/s) and FRBC (C, 22.4 +/- 5.5 vs. CHF, 15.2 +/- 1.2 RBCs/s) were reduced (both P < 0.05) in CHF vs. C muscle. Contractions significantly (both P < 0.05) elevated VRBC (C, 428 +/- 47 vs. CHF, 222 +/- 15 microm/s) and FRBC (C, 44.3 +/- 5.5 vs. CHF, 24.0 +/- 1.2 RBCs/s) in C and CHF muscle; however, both remained significantly lower in CHF than C. The time to 50% of the final response was slowed (both P < 0.05) in CHF compared with C for both VRBC (C, 8 +/- 4; CHF, 56 +/- 11 s) and FRBC (C, 11 +/- 3; CHF, 65 +/- 11 s). Capillary hematocrit increased with contractions in C and CHF muscle but was not different (P > 0.05) between CHF and C. Thus CHF impairs diffusive and conductive O2 delivery across the rest-to-contractions transition in rat skeletal muscle, which may help explain the slowed O2 uptake on-kinetics manifested in CHF patients at exercise onset.

Algorithms↗
PubMed2006

The effect of surface electrical stimulation on hyolaryngeal movement in normal individuals at rest and during swallowing.

Surface electrical stimulation is currently used in therapy for swallowing problems, although little is known about its physiological effects on neck muscles or swallowing. Previously, when one surface electrode placement was used in dysphagic patients at rest, it lowered the hyolaryngeal complex. Here we examined the effects of nine other placements in normal volunteers to determine 1) whether movements induced by surface stimulation using other placements differ, and 2) whether lowering the hyolaryngeal complex by surface electrical stimulation interfered with swallowing in healthy adults. Ten bipolar surface electrode placements overlying the submental and laryngeal regions were tested. Maximum tolerated stimulation levels were applied at rest while participants held their mouths closed. Videofluoroscopic recordings were used to measure hyoid bone and subglottic air column (laryngeal) movements from resting position and while swallowing 5 ml of liquid barium, with and without stimulation. Videofluoroscopic recordings of swallows were rated blind to condition using the National Institutes of Health-Swallowing Safety Scale. Significant (P < 0.0001) laryngeal and hyoid descent occurred with stimulation at rest. During swallowing, significant (P <or= 0.01) reductions in both the larynx and hyoid bone peak elevation occurred during stimulated swallows. The stimulated swallows were also judged less safe than nonstimulated swallows using the National Institutes of Health-Swallowing Safety Scale (P = 0.0275). Because surface electrical stimulation reduced hyolaryngeal elevation during swallowing in normal volunteers, our findings suggest that surface electrical stimulation will reduce elevation during swallowing therapy for dysphagia.

Adult↗
PubMed2004

Rest insertion combined with high-frequency loading enhances osteogenesis.

Mechanical loading can significantly affect skeletal adaptation. High-frequency loading can be a potent osteogenic stimulus. Additionally, insertion of rest periods between consecutive loading bouts can be a potent osteogenic stimulus. Thus we investigated whether the insertion of rest-periods between short-term high-frequency loading bouts would augment adaptation in the mature murine skeleton. Right tibiae of skeletally mature (16 wk) female C57BL/6 mice were loaded in cantilever bending at peak of 800 microepsilon, 30 Hz, 5 days/wk for 3 wk. Left tibiae were the contralateral control condition. Mice were randomly assigned into one of two groups: continuous high-frequency (CT) stimulation for 100 s (n = 9), or 1-s pulses of high-frequency stimuli followed by 10 s of rest (RI) for 100 s (n = 9). Calcein labels were administered on days 1 and 21; label incorporation was used to histomorphometrically assess periosteal and endosteal indexes of adaptation. Periosteal surface referent bone formation rate (pBFR/BS) was significantly enhanced in CT (>88%) and RI (>126%) loaded tibiae, relative to control tibiae. Furthermore, RI tibiae had significantly greater pBFR/BS, relative to CT tibiae (>72%). The endosteal surface was not as sensitive to mechanical loading as the periosteal surface. Thus short-term high-frequency loading significantly elevated pBFR/BS, relative to control tibiae. Furthermore, despite the 10-fold reduction in cycle number, the insertion of rest periods between bouts of high-frequency stimuli significantly augmented pBFR/BS, relative to tibiae loaded continually. Optimization of osteogenesis in response to mechanical loading may underpin the development of nonpharmacological regiments designed to increase bone strength in individuals with compromised bone structures.

Adaptation, Physiological↗
PubMed2002

Skeletal muscle capillary hemodynamics from rest to contractions: implications for oxygen transfer.

Muscle contractions evoke an immediate rise in blood flow. Distribution of this hyperemia within the capillary bed may be deterministic for muscle O(2) diffusing capacity and remains unresolved. We developed the exteriorized rat (n = 4) spinotrapezius muscle for evaluation of capillary hemodynamics before (rest), during, and immediately after (post) a bout of twitch contractions to resolve (second-by-second) alterations in red blood cell velocity (V(RBC)) and flux (f(RBC)). Contractions increased (all P < 0.05) capillary V(RBC) (rest: 270 +/- 62 microm/s; post: 428 +/- 47 microm/s), f(RBC) (rest: 22.4 +/- 5.5 cells/s; post: 44.3 +/- 5.5 cells/s), and hematocrit but not the percentage of capillaries supporting continuous RBC flow (rest: 84.0 +/- 0.7%; post: 89.5+/-1.4%; P > 0.05). V(RBC) peaked within the first one or two contractions, whereas f(RBC) increased to an initial short plateau (first 12-20 s) followed by a secondary rise to steady state. Hemodynamic temporal profiles were such that capillary hematocrit tended to decrease rather than increase over the first approximately 15 s of contractions. We conclude that contraction-induced alterations in capillary RBC flux and distribution augment both convective and diffusive mechanisms for blood-myocyte O(2) transfer. However, across the first 10-15 s of contractions, the immediate and precipitous rise in V(RBC) compared with the biphasic and prolonged increase of f(RBC) may act to lower O(2) diffusing capacity by not only reducing capillary transit time but by delaying the increase in the instantaneous RBC-to-capillary surface contact thought crucial for blood-myocyte O(2) flux.

Animals↗
PubMed2004

Pyruvate shuttling during rest and exercise before and after endurance training in men.

We describe the isotopic exchange of lactate and pyruvate after arm vein infusion of [3-(13)C]lactate in men during rest and exercise. We tested the hypothesis that working muscle (limb net lactate and pyruvate exchange) is the source of the elevated systemic lactate-to-pyruvate concentration ratio (L/P) during exercise. We also hypothesized that the isotopic equilibration between lactate and pyruvate would decrease in arterial blood as glycolytic flux, as determined by relative exercise intensity, increased. Nine men were studied at rest and during exercise before and after 9 wk of endurance training. Although during exercise arterial pyruvate concentration decreased to below rest values (P < 0.05), pyruvate net release from working muscle was as large as lactate net release under all exercise conditions. Exogenous (arterial) lactate was the predominant origin of pyruvate released from working muscle. With no significant effect of exercise intensity or training, arterial isotopic equilibration [(IE(pyruvate)/IE(lactate)).100%, where IE is isotopic enrichment] decreased significantly (P < 0.05) from 60 +/- 3.1% at rest to an average value of 12 +/- 2.7% during exercise, and there were no changes in femoral venous isotopic equilibration. These data show that 1). the isotopic equilibration between lactate and pyruvate in arterial blood decreases significantly during exercise; 2). working muscle is not solely responsible for the decreased arterial isotopic equilibration or elevated arterial L/P occurring during exercise; 3). working muscle releases similar amounts of lactate and pyruvate, the predominant source of the latter being arterial lactate; 4). pyruvate clearance from blood occurs extensively outside of working muscle; and 5). working muscle also releases alanine, but alanine release is an order of magnitude smaller than lactate or pyruvate release. These results portray the complexity of metabolic integration among diverse tissue beds in vivo.

Adult↗
PubMedDate not supplied

Inhibition of nitric oxide synthesis by systemic N(G)-monomethyl-L-arginine administration in humans: effects on interstitial adenosine, prostacyclin and potassium concentrations in resting and contracting skeletal muscle.

We examined whether the formation or the release of the vasodilators adenosine, prostacyclin (PGI(2)) and potassium (K(+)) increase in skeletal muscle interstitium in response to nitric oxide synthase (NOS) inhibition. Five subjects performed one-legged knee extensor exercise at 30 W without (controls) and with prior N(G)-nitro-L-arginine methyl ester (L-NAME) infusion (4 mg/kg, intravenously). Samples from the interstitial fluid were obtained at rest, during exercise and after exercise with the microdialysis technique. Interstitial adenosine in controls increased (p<0.05) from 0.11+/-0.03 micromol/l at rest to 0.48 +/-0.06 micromol/l during exercise. Interstitial adenosine during exercise in L-NAME was similar (p>0.05) to controls. The 6-keto-prostaglandin F1alpha concentration in controls was 1.17+/-0.20 ng/ml at rest and increased (p<0.05) to 1.97+/-0.30 ng/ml during exercise and was further elevated (p<0.05) to 2.76+/-0.38 ng/ml after exercise and these concentrations were not different (p>0.05) in L-NAME. The interstitial K(+) concentration in controls increased (p< 0.05) from 4.1+/-0.1 mmol/l at rest to 9.5+/-0.5 mmol/l during exercise. The interstitial K(+) concentration during exercise (6.7+/- 0.4 mmol/l) was lower (p<0.05) in L-NAME than in controls. The present findings demonstrate that the muscle interstitial concentrations of adenosine, PGI(2) and K(+) during exercise are not increased with systemic NOS inhibition. Thus, the lack of effect of NOS inhibition on the rate of blood flow to contracting human skeletal muscle does not appear to be due to compensatory formation or release of adenosine, PGI(2) and K(+) in the muscle interstitium. The present study also supports a role for PGI(2) in the regulation of blood flow during exercise.

6-Ketoprostaglandin F1 alpha↗
PubMed1998

Aberrant functional organization in schizophrenia: analysis of EEG coherence during rest and photic stimulation in drug-naive patients.

EEG coherence provides a measure of functional correlations between two EEG signals. The present study was conducted to examine intrahemispheric EEG coherence at rest and during photic stimulation (PS) in 18 drug-naive patients with paranoid schizophrenia and 30 control subjects. Compared with the controls, the schizophrenic patients had significantly higher intrahemispheric coherence of the resting EEG for the delta band, although no significant group differences were found for other frequency bands. EEG analysis during PS showed that the patients also had significantly higher EEG coherence over the left posterior regions. In this study, we also examined the changes in intrahemispheric coherence from rest to the stimulus condition (i.e., PS-related coherence reactivity); the patients were found to show significantly smaller changes, with significant group differences being also confined to the posterior regions in the left hemisphere. These findings provide evidence that schizophrenic patients have abnormal EEG coherence in both resting and stimulus conditions and suggest more diffuse, undifferentiated functional organization within hemispheres. In addition, diminished coherence reactivity suggests a failure of PS-related functional reorganization in schizophrenia.

Adult↗
PubMed2002

Higher LDL oxidation at rest and after a rugby game in weekend warriors.

BACKGROUND/AIM: Weekend warriors (WW), people who only exercise vigorously once a week, are a fast-growing population. The present study investigates LDL oxidation and activities of antioxidant enzymes in WW (n = 6) at rest and after a rugby game. The results are compared with those of sedentary controls (CON, n = 10) and trained rugby players (TR, n = 15). METHODS: LDL + VLDL conjugated dienes (CD) and thiobarbituric acid reactive substances (TBARS) as well as erythrocyte superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities were analyzed in WW and TR groups before and after a rugby game. RESULTS: The WW showed higher LDL+VLDL CD and TBARS levels than TR and CON groups at rest (p < 0.05). LDL+VLDL CD and TBARS were also significantly higher in the WW group than in the TR group after exercise (p < 0.05). Both WW and TR groups showed significant exercise-induced elevations in LDL+VLDL TBARS (p < 0.05), with the WW having higher degrees of increase (15.8 +/- 7.9 vs. 6.3 +/- 9.0%, WW group vs. TR group; p < 0.05). Erythrocyte SOD and GPx activities at rest were similar in all three groups. CONCLUSION: These results suggest that WW may have a higher LDL oxidation than TR and CON persons at rest and higher exercise-induced LDL oxidation levels than TR athletes.

Adult↗
PubMed2007

A comparison of myocardial perfusion gated SPECT studies obtained at rest and after stress.

OBJECTIVE: To perform a comparison between post-stress and rest gated single-photon emission computer tomography (SPECT) myocardial perfusion imaging (MPI) studies to assess post-stress stunning and the variables underlying this phenomenon. SUBJECTS AND METHODS: This was a prospective study of 318 consecutive adult patients undergoing stress and rest gated SPECT using a 2-day (99m)Tc-tetrofosmin protocol. Bruce protocol treadmill stress (n = 93) or i.v. dipyridamole pharmacologic stress (n = 225) were used as stressors. Ejection fractions (EF) and left ventricular (LV) end-diastolic (EDV) and end-systolic volumes (ESV) were calculated using the Cedars Sinai Quantitative Gated SPECT software. Perfusion defects were visually scored using a 20-segment model to obtain summed stress scores. Statistical analysis was performed by applying paired t test and multi-regression. Statistically significant (p < 0.05) paired differences between post-stress and rest EF and ESV and type of stressing were noted. RESULTS: Analysis of patient groups based on the type of stress showed significantly low EF on post-stress studies for both treadmill and dipyridamole stressing and also significantly high ESV on post-stress studies for dipyridamole. Multi-regression analysis using differences in post-stress and rest EF, EDV and ESV as dependent and summed stress scores, type of stress, delay time, previous myocardial infarction and size of LV as independent variables showed statistically significant associations between high summed stress scores (>13) and size of post-stress LV for EDV and ESV differences. High volumes were noted on post-stress studies. The magnitudes of the observed differences were well within the reproducibility of LV volume calculations. CONCLUSIONS: Patients showing stunning had significant ischemia or a dilated LV. The stunning manifested as high EDV and ESV differences. The magnitude of the differences observed in EF and LV volumes were not clinically significant.

Adult↗
PubMed2000

Therapeutic angiogenesis with recombinant fibroblast growth factor-2 improves stress and rest myocardial perfusion abnormalities in patients with severe symptomatic chronic coronary artery disease.

BACKGROUND: We report the effects of the administration of recombinant fibroblast growth factor-2 (rFGF-2) protein on myocardial perfusion using single photon emission computed tomography imaging in humans with advanced coronary disease. METHODS AND RESULTS: A total of 59 patients with coronary disease that was not amenable to mechanical revascularization underwent intracoronary (n=45) or intravenous (n=14) administration of rFGF-2 in ascending doses. Changes in perfusion were evaluated at baseline and again at 29, 57, and 180 days after rFGF-2 administration. In this uncontrolled study, perfusion scans were analyzed by 2 observers who were blinded to patient identity and test sequence; scans were displayed in random order, with scans from nonstudy patients randomly interspersed to enhance blinding. Combining all dose groups, a reduction occurred in the per-segment reversibility score (reflecting the magnitude of inducible ischemia) from 1.7+/-0.4 at baseline to 1.1+/-0.6 at day 29 (P:<0.001), 1.2+/-0.7 at day 57 (P:<0.001), and 1.1+/-0.7 at day 180 (P:<0.001). The 37 patients with evidence of resting hypoperfusion had evidence of improved resting perfusion: their per-segment rest perfusion score of 1.5+/-0. 5 at baseline decreased to 1.0+/-0.8 at day 29 (P:<0.001), 1.0+/-0.8 at day 57 (P:=0.003), and 1.1+/-0.9 at day 180 (P:=0.11). CONCLUSIONS: These preliminary data suggest that the administration of rFGF-2 to patients with advanced coronary disease resulted in an attenuation of stress-induced ischemia and an improvement in resting myocardial perfusion; these findings are consistent with a favorable effect of therapeutic angiogenesis.

Coronary Disease↗
PubMed1977

Thallium-201 myocardial perfusion imaging at rest and during exercise. Comparative sensitivity to electrocardiography in coronary artery disease.

The sensitivity of myocardial perfusion imaging (MPI) using thallium-201 injected both at rest and during peak exercise was compared to simultaneously recorded 12 lead electrocardiography (ECG) for the detection of transient ischemia in 20 normal subjects and 63 patients with coronary artery disease (CAD). No significant perfusion defects or ECG changes were seen on either the rest or exercise studies in any of the normal subjects. Fifty-six percent of patients with CAD developed new perfusion defects with exercise compared to 38% who developed ischemic ST-segment depression (P less than 0.02). However, when chest pain and/or ST depression were considered indices of ischemia, the sensitivity of exercise testing and thallium-201 MPI was similar. The increased sensitivity of MPI compared to ST-segment depression on the ECG was due to patients with baseline ECG abnormalities and those who failed to achieve 85% of predicted maximum heart rate with exercise. Analysis of the exercise results according to the extent of coronary artery disease revealed a progressive increase in both positive ECGs and MPI with the number of vessels involved. In patients with single vessel disease the MPI was more sensitive than the ECG (P less than 0.02). The combination of the rest and exercise ECG, MPI and chest pain during exercise failed to identify 11% of patients with CAD. Exercise thallium-201 MPI is a useful adjunct to conventional exercise testing particularly when evaluating patients with abnormal resting ECGs, those who develop ventricular conduction defects of arrhythmias during exercise, and those who fail to achieve their predicted heart rate because of fatigue or breathlessness.

Adult↗
PubMed1981

Acute and long-term effects of vasodilator therapy on resting and exercise hemodynamics and exercise tolerance.

The acute hemodynamic response to vasodilators in patients with chronic heart failure has been well characterized, but less is known about the long-term hemodynamic effects of vasodilator therapy. We measured hemodynamic variables at rest and during upright exercise in 11 patients during the initiation of therapy with oral hydralazine and sublingual isosorbide dinitrate and, in eight of these, after 3 months of continuous treatment. Marked initial increases in resting cardiac output and stroke volume and reductions in wedge pressure were sustained during chronic therapy. Similarly, the early improvement in exercise hemodynamic measurements persisted in most subjects. Exercise tolerance, quantified as the maximum duration of treadmill exercise, increased modestly (7.7 +/- 2.6 to 8.9 +/- 3.3 minutes, 0.05 less than p less than 0.10) after several days on vasodilators and further (10.2 +/- 3.7 minutes, p less than 0.01) during long-term treatment. The acute hemodynamic effects of vasodilator therapy at rest or during exercise did not correlate well with the changes in exercise tolerance. Our findings suggest that the combination of hydralazine and isosorbide dinitrate improves cardiac performance at rest and during exercise in patients with chronic heart failure and that this improvement persists during chronic therapy. In most patients, this hemodynamic improvement is accompanied by greater exercise tolerance.

Acute Disease↗
PubMed1984

The effect of antihypertensive drug treatment on mortality in the presence of resting electrocardiographic abnormalities at baseline: the HDFP experience. The Hypertension Detection and Follow-up Program Cooperative Research Group.

The Hypertension Detection and Follow-up Program (HDFP) reported a significant reduction in 5 year mortality from all causes in its intensively treated stepped care group compared with its referred care group (p less than .01). In stratum I (mean baseline diastolic blood pressure 90 to 104 mm Hg) mortality in the stepped care group was 20.3% lower than that in the referred care group (p less than .01). For persons in this stratum not on antihypertensive drugs at baseline and free of major target organ damage, mortality in the stepped care group was 28.6% lower than that in the referred care group (p less than .01). Publication of the results of Multiple Risk Factor Intervention Trail (MRFIT), indicating possibly increased mortality in special intervention hypertensive participants with resting electrocardiographic (ECG) abnormalities, prompted further analyses of the HDFP data to determine whether stepped care drug treatment in stratum I patients with resting ECG abnormalities was associated with a similar outcome. Of the 7825 HDFP participants in stratum I, 5173 met MRFIT eligibility criteria and qualified as a subgroup comparable to the MRFIT "mild" hypertensives, 1963 with and 3210 without evidence of resting ECG abnormalities at baseline. In the subgroup without resting ECG abnormalities, mortality rates for coronary heart disease, major cardiovascular diseases, and for all causes were consistently lower in the stepped care group than in the referred care group. This finding was consistent with the MRFIT results.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗