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Biomedical subjects

D S Miles

Publications and source records attributed to D S Miles.

At least 37 records · Page 2Linked to original sources
PubMed1988

Running-induced changes in lung function are not altered by acute moderate hypoxia.

The purpose of this study was to describe the acute changes in pulmonary function and volumes induced by running in a simulated normobaric hypoxic environment. Eleven men (X- = 26 years, 78 kg) ran 5 miles (run time approximately equal to 40 min) under normoxic (N) and hypoxic (H) conditions. A PO2 Aerobic Exerciser was used to approximate an altitude of 2286 m (PIO2 = 113 mm Hg). Impedance cardiography was used to measure cardiac output and segmental transthoracic impedance (Zo) was used to identify thoracic fluid shifts. Similar reductions in vital capacity (7%) and increases in residual volume (10%) occurred after the N and H runs with no change in total lung capacity. Flow rates breathing air or He/O2, closing volume, and closing capacity did not change. The DLCO breathhold maneuver caused a significant fall in pulmonary blood flow after running but diffusing capacity appeared to be unaffected. No changes occurred in Zo at the apex, middle, or base of the lung after either run. The hypoxic pulmonary pressor response failed to modify the pulmonary changes observed after equivalent normoxic exercise. The lung volume changes subsequent to either run were due to expiratory limitation. Previous speculation of an exercise-induced interstitial edema could not be confirmed.

Adult↗
PubMed1987

Central and peripheral hemodynamics during maximal leg extension exercise.

The purpose of this study was to examine the central and peripheral hemodynamic adaptations to maximal leg extension exercise. Seventeen men (X = 25 years, 84 kg) performed leg extension exercise (Universal equipment) for 12 repetitions (90s) to fatigue. Each repetition consisted of a 3s lifting motion, 1s pause, and 3s lowering motion. Impedance cardiography was used to measure stroke volume (SV), cardiac output (Q), systolic time intervals, and impedance contractility indices on a beat-by-beat basis. There were significant increases in systolic, diastolic, mean arterial pressure, total peripheral resistance, and HR during exercise. The mean Q remained similar throughout the protocol. SV decreased even though indices of myocardial performance indicated an enhancement of contractility. The magnitude of Q and SV were dependent upon the phase of leg extension. SV and Q during the lifting portions of the exercise were smaller than the lowering portions. The differences in SV and Q during the concentric and eccentric phases of the exercise most likely reflect the large static forces in exercising muscle which impeded venous return and increased afterload.

Adolescent↗
PubMed1986

Interpretation of changes in DLCO and pulmonary function after running five miles.

The purpose of this study was to evaluate changes in pulmonary function after running five miles. Of particular interest was the reaffirmation of the previously reported 'uncoupling' or dissociation of pulmonary diffusing capacity (DLCO) and cardiac output (Q) after moderate or strenuous exercise. Cardiopulmonary assessments were made on eight runners before and after completing three separate five mile runs. There were significant reductions in vital capacity (5.7%) and volume at closing with increases in residual volume (22.5%) and closing capacity post-run. Although DLCO did not change, significant change in cardiac output occurred during the DLCO 10 sec breathhold maneuver. The pre-run DLCO maneuver produced a fall in stroke volume (SV) with an increase in HR while maintaining Q. The post-run Q fell during the DLCO maneuver due to a fall in SV with HR remaining constant. The primary basis for previous speculation of the development of a transient pulmonary edema during exercise has been the failure of DLCO to increase immediately after exercise when HR and presumably Q is elevated. To avoid any misinterpretation of changes in DLCO produced by exercise, Q should be measured at the time of the DLCO determination. Our findings suggest that values for DLCO post-exercise are entirely appropriate for the pulmonary blood flow at the time of the DLCO maneuver.

Adult↗
PubMed1986

Metabolic responses of women to exercise attributable to long term use of a manual wheelchair.

The purpose of this study was to determine the effects of long term use of a manual wheelchair by wheelchair-confined women (means = 14.6 years) on physiological responses to wheelchair ergometry. Six experimental subjects were compared to six able bodied women during maximal exercise as well as submaximal wheelchair ergometry at 50 and 80% of peak VO2. The wheelchair dependent women achieved higher power outputs, greater efficiency at the higher submaximal workload, less metabolic acidosis during submaximal exercise as well as less ventilatory stress. There was no significant difference in peak VO2 between the two groups of women. Because these were not athletically trained women, it was concluded that the long term use of a manual wheelchair leads to physiological adaptations favourable to the daily requirements of wheelchair locomotion.

Acid-Base Equilibrium↗
PubMed1986

Assessment of peripheral hemodynamics using impedance plethysmography.

Impedance plethysmography (IPG) is a safe, noninvasive method for measuring peripheral hemodynamics. The purpose of this article is to describe the IPG technique and its potential use by physical therapists in making hemodynamic evaluations. Impedance plethysmography requires the attachment of four circumferential Mylar band electrodes around a limb. We use a cardiograph to introduce a 4-mA current (I) at a frequency of 100 kHz in the two outer electrodes. The voltage (V) is sensed in the two center electrodes, and the resulting impedance (Z) is calculated using Ohm's law (Z = V/I). Arterial blood flow can be calculated using an impedance-related volume conduction equation. Impedance plethysmography has been shown to be economical, and any limb or limb segment can be evaluated. Applications are presented for the assessment of arterial blood flow, peripheral arterial disease, deep vein thrombosis, and venous insufficiency. Impedance plethysmography offers the physical therapist a safe and relatively simple technique to assess the peripheral vascular status of the patient.

Chronic Disease↗
PubMed1986

Evaluation of impedance cardiography in the canine pup.

This study evaluated the use of the noninvasive technique of impedance cardiography to assess central hemodynamics in an animal model similar in size to the neonate. Seven canine pups 5-6 wk of age, with an average weight of 2.2 kg, were studied. To alter cardiac output (Q), the pups were given 12 and 8% O2 to breathe, which produced an arterial PO2 of 30 and 21 Torr, respectively. Q was obtained simultaneously by impedance and thermal dilution under both normoxic and hypoxic conditions. The average Q measured by impedance and thermal dilution were within 10% agreement and moderately correlated (r = 0.76). Impedance Q and stroke volume (SV) averaged 201 ml X min-1 X kg-1 and 2.8 ml, respectively. Thermal dilution Q and SV averaged 212 ml X min-1 X kg-1 and 2.9 ml, respectively. Individual responses to the hyoxemia were variable, but the impedance technique appeared to measure these individual responses as well as the thermal-dilution technique. These findings demonstrate that impedance cardiography may be suitable to assess either the absolute or relative changes in central hemodynamics. The use of this technique in critical care neonatal and pediatric medicine seems justified.

Animals↗
PubMed1986

Oscillatory cardiopulmonary effects of high-frequency jet ventilation.

The cardiovascular effects of high-frequency jet ventilation (HFJV) were compared with conventional volume ventilation in the anesthetized dog. A unique effect of HFJV on stroke volume and cardiac output was observed when stroke volume was analyzed on a beat-by-beat basis with impedance cardiography. A pronounced amplitude modulation of stroke volume, as well as of pulmonary and arterial pressure, occurred when the frequency of the HFJV approached the heart rate. The beat frequency of these amplitude oscillations was equal to that predicted based upon the frequency of the HFJV and the heart rate. Cardiac outputs obtained by techniques which average several beats will not detect these oscillations in cardiac output. These findings suggest that HFJV can generate an oscillation in thoracic hemodynamics which affects ventricular output in a similar manner.

Animals↗
PubMed1986

The combined effects of hypoxemia and mechanical ventilation on renal function.

The combined effects of hypoxemia and mechanical ventilation on renal function were investigated in anesthetized dogs. Spontaneously breathing dogs (S) and dogs mechanically ventilated with a volume-ventilator (V) were made hypoxemic by breathing hypoxic gas to achieve PaO2 values of 35 and 22 mm Hg. At a PaO2 of 35 mm Hg, urine output and sodium excretion were increased in both groups. These responses closely followed the blood pressure response, which was greater in the V group. Renal blood flow (RBF), glomerular filtration rate (GFR), and fractional sodium excretion (FNA) were unchanged. At a PaO2 of 22 mm Hg, both groups demonstrated a reduction in urine flow, sodium excretion, FNA, RBF, and GFR. However, the mechanism involved was different and ventilator-dependent. At this low PaO2, arterial blood pressure was reduced in the S group with no change in renal resistance, while blood pressure increased in the V group with a marked increase in renal resistance as a result of the modification of the cardiovascular effects of lung inflation reflexes by mechanical ventilation. These results indicate that renal function is well-maintained at low PaO2 values (35 mm Hg) and reduced at more severe hypoxemia, mainly in response to systemic hemodynamics.

Animals↗
PubMed1984

Central hemodynamics during progressive upper- and lower-body exercise and recovery.

The purpose of this study was to compare stroke volume (SV) and myocardial contractility responses during and immediately after upper- and lower-body exercise. Nine men (mean 28 yr, 78 kg) completed progressive intensity discontinuous tests on both an arm crank and cycle ergometer. Exercise for each power output (PO) was 7 min with 20-min rest periods interspersed. Impedance cardiography was used to measure cardiac output (Q), SV, and contractility on a beat-by-beat basis during exercise and a 15-s recovery period. Q increased linearly, and total peripheral resistance decreased exponentially with increasing PO levels. During recovery from exercise, the Q and heart rate (HR) values decreased immediately at all PO levels. When the exercise VO2 exceeded 1.0 1 X min-1, SV fell significantly during recovery for both exercise modes. In general, the recovery myocardial contractility indices remained similar to exercise values. It was concluded that immediately after low intensities of exercise, Q decreases because of a fall in HR. After moderate- and high-intensity exercise, Q decreases because of a fall in both HR and SV.

Adult↗
PubMed1984

Metabolic, hemodynamic, and respiratory responses to performing cardiopulmonary resuscitation.

The purpose of this study was to evaluate the cardiorespiratory demands inherent to the maintenance of continuous one- and two-man cardiopulmonary resuscitation (CPR) for 10 min. Ten male paramedics (X age = 26 yrs) certified to perform CPR participated. Each subject assumed the three possible roles for administering CPR: ventilator, compressor, and one-man technique. Cardiorespiratory responses were determined by impedance cardiography and open-circuit spirometry at 2 min intervals while performing CPR with a resuscitation manikin. Left ventricular performance was evaluated by impedance ventricular function indices (VFI) and systolic time intervals (STI). All three roles elicited an increase in oxygen uptake compared to kneeling rest, with the roles of one-man and compressor being the most demanding. There were moderate increases in cardiac output and heart rate during the exercise roles, but stroke volume remained similar to resting values. Pulmonary ventilation increased during exercise, with the greatest increase occurring for the one-man role. STI and impedance VFI reflected an enhanced ventricular performance while performing the roles of one-man and compressor. These findings suggest that the energetic demands placed on the rescuer depend upon the specific role assumed. Properly trained and experienced individuals can perform CPR efficiently for at least 10 min while eliciting only moderate physiological stress.

Adult↗
PubMed1983

Changes in pulmonary diffusing capacity and closing volume after running a marathon.

The purpose of this study was to evaluate changes in lung function after running a marathon. Pulmonary function tests were administered to 8 men before, immediately after, and the day following competition (mean run time = 3 hr 30 min). Subjects completed maximum expiratory flow volume maneuvers breathing air and 80% He/20% O2. Lung volumes were determined by N2 washout and single breath He dilution. Closing volumes (CV) were determined using a single breath O2 test. Pulmonary diffusing capacity (DLCO), pulmonary capillary blood volume (Vc), and membrane diffusing capacity (DM) were measured with the single breath technique. There were no changes in lung volumes or flow rates, except for an increase in FEV1, after the marathon. The He/O2 delta Vmax50, delta Vmax25, and isoflow values were similar pre- compared to post-race. There were significant decreases, however, in DLCO, DM and increases in CV post-race. Vc remained similar to pre-race values. These results suggest that small airways obstruction does not occur after a marathon. The significant increase in alveolar-capillary membrane resistance, however, may reflect the occurrence of subclinical edema. Such a change would decrease lung elastic recoil and could explain the increase in CV.

Adult↗
PubMed1983

Plasma volume shifts during progressive arm and leg exercise.

Upper and lower body exercise was performed to assess the influence muscle mass has on plasma volume (PV) shifts. Nine male subjects (mean = 28 yr) completed a progressive intensity, discontinuous test with an arm crank (AC) and cycle (CY) ergometer. Power output (PO) levels for the AC were 25, 74, 98, and 133 W. PO levels for the CY were 49, 98, 147, and 263 W. At a given submaximal oxygen uptake (VO2), PV efflux was significantly greater for AC compared with CY exercise. When PV efflux was related to the relative intensity of the exercise (ergometer specific % peak VO2), responses were nearly identical. Maximal PV efflux was 18% for both AC and CY exercise. Mean arterial pressure (MAP) was significantly greater for AC compared with CY exercise for a given VO2. MAP plotted against the relative intensity of exercise, however, was similar for both AC and CY exercise. These results suggest that the amount of plasma efflux during exercise is related to the MAP, which is directly related to the relative intensity of the exercise.

Adult↗
PubMed1983

Renal oxygen delivery and consumption during progressive hypoxemia in the anesthetized dog.

The relationship between renal oxygen delivery (RDO2) and function was evaluated during progressive hypoxemia. Seven anesthetized, spontaneously breathing dogs were given progressively lower oxygen concentrations to breathe while monitoring renal O2 consumption (RVO2), renal hemodynamic and excretory function. In addition, basal RVO2 was determined in three models of kidneys without filtration. RDO2 averaged 3648 mumole O2/min/100 g during normoxia. Basal RVO2 averaged 100 mumole O2/min/100 g kidney while total RVO2 was 466 mumole O2/min/100 g kidney during normoxia, leaving 366 mumole O2/min/100 g consumed by those processes involved in tubular transport. During hypoxemia, all renal parameters were well maintained until the lowest PaO2 (24.2 Torr). At this level, total RVO2 and RDO2 were significantly reduced. However, RDO2 remained well above RVO2 throughout hypoxemia. The reduction in RVO2 was a direct result of decreased O2 demand, as glomerular filtration and tubular load were also reduced. This associated decrease in O2 demand and RVO2 was indicated by the fact that the renal (a - v)O2 difference remained low and unchanged (1.9 vol%), fractional sodium excretion was unchanged, and the ratio of tubular sodium reabsorption to RVO2 also remained unchanged (30.8 meq Na/mmole O2). It was concluded that hypoxemia, while reducing both RDO2 and RVO2 at the lowest PaO2 (24.2 Torr), did not functionally impair renal excretory function by limiting RDO2 to the tubular transport processes. A reduction in RBF is far more likely to compromise the RDO2 needed to sustain basal and active transport processes than hypoxemia itself.

Animals↗
PubMed1982

Ventilation and acid-base equilibrium for upper body and lower body exercise.

The purpose of this study was to compare pulmonary ventilation and blood acid-base responses for upper and lower body exercise at a variety of metabolic intensities. Nine male subjects completed a progressive intensity, discontinuous test for arm crank (AC) and cycle (CY) ergometry. During submaximal exercise, oxygen uptake (VO2), pulmonary ventilation (VE), VE/VO2, alveolar ventilation (VA) and blood lactate (LA) values were found to increase, whereas arterial carbon dioxide partial pressure (PCO2) and arterial pH values were found to decrease with increasing power output for both modes of ergometry. Generally, for a given submaximal power output level, VO2, VE, VE/VO2, VA. and LA values were higher, but, PCO2 and pH values were lower for AC compared to CY exercise. During maximal exercise, VO2, VE, VA, LA, and PCO2 values were lower for AC than CY exercise. When VE, VA, LA, PCO2 and pH were expressed in relation to percent of peak VO2 (ergometer specific), nearly identical response patterns were found for both modes of exercise. These results indicate that pulmonary ventilation and blood acid-base responses are dependent upon relative exercise intensity rather than the muscle groups employed.

Acid-Base Equilibrium↗