Biomedical subjects

D R Seals

Publications and source records attributed to D R Seals.

At least 127 records · Page 7Linked to original sources

PubMed1990

Endorphins and exercise: physiological mechanisms and clinical implications.

In this paper we discuss recent experimental and clinical findings which lead us to propose that prolonged rhythmic exercise can activate central opioid systems by triggering increased discharge from mechanosensitive afferent nerve fibers (Group III or A-delta) arising from contracting skeletal muscle. We review evidence that supports the concept that many of the cardiovascular, analgesic, and behavioral effects of exercise are mediated by this mechanism and that the same or similar mechanisms are responsible for the central and peripheral effects of acupuncture. Based on this hypothesis, and supporting evidence from human and animal studies, we suggest a mechanism and a potential therapeutic role for exercise in the treatment of selected patients with disorders as diverse as hypertension, addiction, depression, and anorexia nervosa.

Acupuncture Therapy↗

PubMed1989

Response of upper limb blood flow to handgrip exercise after Blalock-Taussig operation (for tetralogy of Fallot) or subclavian flap operation (for aortic isthmic coarctation).

To evaluate the effects of long-term reductions in perfusion pressure on blood flow responses to increased functional demand, 5 patients (aged 12 to 26 years) without normal aortic to subclavian artery blood flow to 1 arm as a result of surgery to treat congenital heart disease were studied. Five age- and sex-matched healthy (control) subjects were also studied. In the patients, forearm blood flow was not different in the surgical and normal arms at rest (3.6 +/- 0.6 vs 4.0 +/- 0.7 ml/min/100 ml, respectively, mean +/- standard error, difference not significant) despite lower systolic blood pressure in the surgical arm (87 +/- 2 vs 115 +/- 2 mm Hg, p less than 0.05). The increases in heart rate, systolic blood pressure, forearm electromyographic activity (index of muscle fatigue) and postexercise forearm blood flow (index of muscle oxygen deficit) were not different in response to 2.5 minutes of submaximal rhythmic handgrip exercise (50% of maximal force) performed with the surgical versus the normal arms. Peak forearm blood flow elicited by combined ischemia and maximal isometric handgrip exercise was not significantly different in surgical and normal arms in the group as a whole (39 +/- 4 vs 43 +/- 3 ml/min/100 ml, difference not significant), although some bilateral deficit (20 to 38%) was observed in 2 patients. No bilateral differences were observed in the control subjects under any condition. The finding of normal physiologic adjustments to submaximal rhythmic handgrip exercise with the surgical arm suggests that oxygen delivery during exercise was adequate.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Physiological↗

PubMed1989

Reflex stimulation of sympathetic outflow during rhythmic exercise in humans.

The aim of this study was to determine whether a chemically generated reflex arising in nonischemic skeletal muscle normally increases sympathetic outflow during rhythmic exercise. To accomplish this aim, we recorded muscle sympathetic nerve activity (MSNA, peroneal nerve) in conscious humans during exercise interventions designed to alter the relationship between muscle blood flow and metabolic demand. Under normal conditions, MSNA increased during moderate but not during mild levels of rhythmic handgrip (0.67 Hz) and one-arm cycling (0.83 Hz). MSNA remained elevated when the moderate level of rhythmic handgrip was followed by forearm vascular occlusion, a maneuver that sustains muscle chemoreflex stimulation. Complete arm vascular occlusion was needed to increase MSNA during mild arm cycling, whereas even partial vascular occlusion greatly amplified the stimulation of MSNA normally produced by the moderate level of arm cycling. We conclude that a chemically generated reflex arising in nonischemic working muscle plays an important role in the normal activation of sympathetic discharge to nonexercising leg muscles during moderate but not during mild levels of rhythmic arm exercise.

Adult↗

PubMed1989

Sympathetic activation is associated with increases in EMG during fatiguing exercise.

The purpose of this study was to test the hypothesis that efferent sympathetic neural discharge is coupled with the development of muscle fatigue during voluntary exercise in humans. In 12 healthy subjects (aged 20-34 yr) we measured heart rate (HR), arterial blood pressure (AP), and noncontracting, skeletal muscle sympathetic nerve activity (MSNA) in the leg (peroneal nerve) before (control) and during each of three trials of submaximal (30% of maximum) isometric handgrip exercise performed to exhaustion. In six of the subjects of eletromyographic (EMG) activity of the exercising forearm was also measured. HR and AP increased significantly (P less than 0.05) in the 1st min of exercise in all trials. In contrast, neither MSNA nor EMG activity increased significantly above control during the 1st min of exercise, but both parameters subsequently increased in a progressive and parallel manner (P less than 0.05). The overall correlation coefficient between MSNA and EMG activity (144 observations) was 0.85 (P less than 0.001). With successive trials the magnitudes of the increases in HR, AP, MSNA, and EMG activity were greater at any absolute point in time during exercise. These results indicate that sympathetic activation to noncontracting skeletal muscle is directly related to the development of muscle fatigue (as assessed by the change in EMG) during prolonged isometric exercise in humans. Furthermore, our findings demonstrate that previous fatiguing contractions alter the time course of the sympathetic neural adjustments to exercise.

Adult↗

PubMed1989

Hypoxemia raises muscle sympathetic activity but not norepinephrine in resting humans.

The experimental objective was to determine whether moderate to severe hypoxemia increases skeletal muscle sympathetic nervous activity (MSNA) in resting humans without increasing venous plasma concentrations of norepinephrine (NE) and epinephrine (E). In nine healthy subjects (20-34 yr), we measured MSNA (peroneal nerve), venous plasma levels of NE and E, arterial blood pressure, heart rate, and end-tidal O2 and CO2 before (control) and during breathing of 1) 12% O2 for 20 min, 2) 10% O2 for 20 min, and 3) 8% O2 for 10 min--in random order. MSNA increased above control in five, six, and all nine subjects during 12, 10, and 8% O2, respectively (P less than 0.01), but only after delays of 12 (12% O2) and 4 min (8 and 10% O2). MSNA (total activity) rose 83 +/- 20, 260 +/- 146, and 298 +/- 109% (SE) above control by the final minute of breathing 12, 10, and 8% O2, respectively. NE did not rise above control at any level of hypoxemia; E rose slightly (P less than 0.05) at one time only with both 10 and 8% O2. Individual changes in MSNA during hypoxemia were unrelated to elevations in heart rate or decrements in blood pressure and end-tidal CO2--neither of which always fell. We conclude that in contrast to some other sympathoexcitatory stimuli such as exercise or cold stress, moderate to severe hypoxemia increases leg MSNA without raising plasma NE in resting humans.

Adult↗

PubMed1989

Influence of physical training on heart rate variability and baroreflex circulatory control.

Nineteen males (aged 45-68 yr) were studied before and after either a period of regular endurance exercise [walk/jog 3-4 days/wk for 30 +/- 1 (SE) wk, n = 11] or unchanged physical activity (38 +/- 2 wk, n = 8) (controls) to determine the influence of physical training on cardiac parasympathetic (vagal) tone and baroreflex control of heart rate (HR) and limb vascular resistance (VR) at rest in middle-aged and older men. Training resulted in a marked increase in maximal O2 uptake (31.6 +/- 1.2 vs. 41.0 +/- 1.8 ml.kg-1.min-1, 2.56 +/- 0.16 vs. 3.20 +/- 0.18 l/min, P less than 0.05) and small (P less than 0.05) reductions in body weight (81.2 +/- 3.5 vs. 78.7 +/- 4.0 kg) and body fat (23.8 +/- 1.3 vs. 20.9 +/- 1.3%). HR at rest was slightly, but consistently, lower after training (63 +/- 2 vs. 58 +/- 1 beats/min, P less than 0.05). In general, HR variability (index of cardiac vagal tone) was greater after training. Chronotropic responsiveness to either brief carotid baroreflex stimulation (neck suction) or inhibition (neck pressure), or to non-specific arterial baroreflex inhibition induced by a hypotensive level of lower body suction, was unchanged after training. In contrast, the magnitude of the reflex increase in forearm VR in response to three levels of lower body suction was markedly attenuated after training (38-59%; P less than 0.05 at -10 and -30 mmHg; P = 0.07 at -20 mmHg). None of these variables or responses was altered over time in the controls. These findings indicate that in healthy, previously sedentary, middle-aged and older men, strenuous and prolonged endurance training 1) elicits large increases in maximal exercise capacity and small reductions in HR at rest, 2) may increase cardiac vagal tone at rest, 3) does not alter arterial baroreflex control of HR, and 4) results in a diminished forearm vasoconstrictor response to reductions in baroreflex sympathoinhibition.

Aged↗

PubMed1989

Sympathetic neural discharge and vascular resistance during exercise in humans.

The purpose of this study was to determine the relationship between changes in efferent muscle sympathetic nerve activity (MSNA) to the lower leg and calf vascular resistance (CVR) during isometric exercise in humans. We made intraneural (microneurographic) determinations of MSNA in the right leg (peroneal nerve) while simultaneously measuring calf blood flow to the left leg, arterial pressure, and heart rate in 10 subjects before (control), during, and after (recovery) isometric handgrip exercise performed for 2.5 min at 15, 25, and 35% of maximal voluntary contraction (MVC). Heart rate and arterial pressure increased above control within the initial 30 s of handgrip at all levels, and the magnitudes of the increases at end contraction were proportional to the intensity of the exercise. In general, neither MSNA nor CVR increased significantly above control levels during handgrip at 15% MVC. Similarly, neither variable increased above control during the initial 30 s of handgrip at 25 and 35% MVC; however, during the remainder of the contraction period, progressive, parallel increases were observed in MSNA and CVR (P less than 0.05). The correlation coefficients relating changes in MSNA to changes in CVR for the individual subjects averaged 0.63 +/- 0.07 (SE) (range 0.30-0.91) and 0.94 +/- 0.06 (range 0.80-0.99) for the 25 and 35% MVC levels, respectively. During recovery, both MSNA and CVR returned rapidly toward control levels. These findings demonstrate that muscle sympathetic nerve discharge and vascular resistance in the lower leg are tightly coupled during and after isometric arm exercise in humans. Furthermore, the exercise-induced adjustments in the two variables are both contraction intensity and time dependent.

Adult↗

PubMed1989

Differential control of forearm and calf vascular resistance during one-leg exercise.

The purpose of this study was to determine whether blood flow (BF) and vascular resistance (VR) are controlled differently in the nonactive arm and leg during submaximal rhythmic exercise. In eight healthy men we simultaneously measured BF to the forearm and calf (venous occlusion plethysmography) and arterial blood pressure (sphygmomanometry) and calculated whole limb VR before (control) and during 3 min of cycling with the contralateral leg at 38, 56, and 75% of peak one-leg O2 uptake (VO2). During the initial phase of exercise (0-1.5 min) at all work loads, BF increased and VR decreased in the forearm (P less than 0.05), whereas calf BF and VR remained at control levels. Thereafter, BF decreased and VR increased in parallel and progressive fashion in both limbs. At end exercise, forearm BF and VR were not different from control values (P greater than 0.05); however, in the calf, BF tended to be lower (P less than 0.05 at 75% peak VO2 only) and VR was higher (23 +/- 9, 44 +/- 14, and 88 +/- 23% above control at 38, 56, and 75% of peak VO2, respectively, all P less than 0.05). In a second series of studies, forearm and calf skin blood flow (laser-Doppler velocimetry) and arterial pressure were measured during the same levels of exercise in six of the subjects. Compared with control, skin BF was unchanged and VR was increased (P less than 0.05) in the forearm by end exercise at all work loads, whereas calf skin BF increased (P less than 0.05) and VR decreased (P less than 0.05). The present findings indicate that skeletal muscle and skin VR are controlled differently in the nonactive forearm and calf during the initial phase of rhythmic exercise with the contralateral leg. Skeletal muscle vasodilation occurs in the forearm but not in the calf; forearm skin vasoconstricts, whereas calf skin vasodilates. Finally, during exercise a time-dependent vasoconstriction occurs in the skeletal muscle of both limbs.

Adult↗

PubMed1989

Influence of muscle mass on sympathetic neural activation during isometric exercise.

The primary purpose of this study was to determine whether the sympathetic neural activation induced by isometric exercise is influenced by the size of the contracting muscle mass. To address this, in nine healthy subjects (aged 19-27 yr) we measured heart rate, systolic arterial blood pressure, and muscle sympathetic nerve activity in the leg (MSNA; peroneal nerve) before (control) and during 2.5 min of isometric handgrip exercise (30% of maximal voluntary force). Exercise was performed with the right and left arms separately and with both arms simultaneously (random order). During exercise, heart rate, systolic pressure, and MSNA increased above control under all conditions (P less than 0.05). For each variable, the magnitudes of the increases from control to the end of exercise were significantly greater when exercise was performed with two arms compared with either arm alone (P less than 0.05). In general, the increases in heart rate, systolic pressure, and MSNA elicited during two-arm exercise were significantly less than the simple sums of the responses evoked during exercise of each arm separately. These findings indicate that the magnitude of the sympathetic neural activation evoked during isometric exercise in humans is determined in part by the size of the active muscle mass. In addition, our results suggest that the sympathetic cardiovascular adjustments elicited during exercise of separate limbs are not simply additive but instead exhibit an inhibitory interaction (i.e., neural occlusion).

Adult↗

PubMed1989

Postexercise hypotension and sympathoinhibition in borderline hypertensive men.

To determine if there would be a decrease in blood pressure after exercise in patients with borderline hypertension and if this decrease would be accompanied by a decrease in sympathetic nerve activity to muscle, we recorded multifiber postganglionic muscle sympathetic activity from the peroneal nerve at rest in nine men with borderline hypertension (age 25 +/- 1 years, mean +/- SEM) before and 60 minutes after 45 minutes of submaximal treadmill exercise. In addition, responses to a cold pressor test, handgrip, and the Valsalva maneuver were recorded before and after exercise. Four subjects were also studied before and after "sham" exercise. Sham exercise had no effect on blood pressure or sympathetic nerve activity whereas resting systolic blood pressure was lower after treadmill exercise in seven subjects (from 136 +/- 4 before to 123 +/- 2 mm Hg 60 minutes after exercise; p less than 0.01). Sixty minutes after exercise, sympathetic nerve activity was lower in all seven subjects (from 19 +/- 2 to 11 +/- 2 bursts/min, p less than 0.015; or from 27 +/- 3 to 14 +/- 2 bursts/100 heartbeats, p less than 0.005) but was slightly increased in the two subjects without postexercise hypotension. Heart rate and pressor and sympathoneural responses to the cold pressor test, handgrip, and the Valsalva maneuver were not altered by prior exercise. When nitroprusside was infused in five subjects to produce a reduction in systolic blood pressure similar to that seen 60 minutes after exercise, this drug increased sympathetic discharge from 37 +/- 6 to 57 +/- 4 bursts/100 heartbeats (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1988

Left ventricular dysfunction after prolonged strenuous exercise in healthy subjects.

To determine whether depressed left ventricular (LV) contractile function can occur after prolonged and strenuous exercise, 12 healthy men, 26 +/- 1 years old (mean +/- standard error of the mean) were studied. The subjects exercised on a treadmill at 69 +/- 1% of maximal O2 uptake until exhaustion (170 +/- 10 minutes). Hemodynamic variables were measured before and 10 minutes after exhausting exercise. Baseline systolic blood pressure decreased from 124 +/- 2 to 113 +/- 3 mm Hg (p less than 0.001) after exhausting exercise. LV end-diastolic diameter, measured by echocardiography, decreased from 51 +/- 1.0 to 47 +/- 1.0 mm (p less than 0.005) but LV end-systolic diameter did not change (34 +/- 1.0 vs 34 +/- 1.0 mm). Both LV fractional shortening and the mean velocity of circumferential fiber shortening decreased (33 +/- 1 vs 28 +/- 1%; p less than 0.01 and 1.09 +/- 0.4 vs 0.97 +/- 0.05 circ/s; p less than 0.025) despite a lower end-systolic wall stress (sigma es = 88 +/- 4 vs 82 +/- 5, X 10(3) dynes/cm2; p less than 0.05) after prolonged exhausting exercise. A repeat bout of exercise of the same intensity but brief in duration (10 minutes) resulted in increases in LV fractional shortening (p less than 0.001) and mean velocity of circumferential fiber shortening (p less than 0.001), and a decrease in LV end-diastolic diameter (50 +/- 1.0 to 48 +/- 1.0 mm; p less than 0.05) at heart rates comparable to those attained after prolonged exhausting exercise. The results suggest that prolonged strenuous exercise may result in impaired LV function in healthy young subjects.

Adult↗

PubMed1988

Cardiovascular adjustments to rhythmic handgrip exercise: relationship to electromyographic activity and post-exercise hyperemia.

The purpose of this study was to examine the association among electromyographic (EMG) activity, recovery blood flow, and the magnitude of the autonomic adjustments to rhythmic exercise in humans. To accomplish this, 10 healthy subjects (aged 23-37 y) performed rhythmic handgrip exercise for 2 min at 5, 15, 25, 40, and 60% of maximal voluntary force. Heart rate and arterial blood pressure were measured at rest (control), during each level of exercise, and for 2 min following exercise (recovery). The rectified, filtered EMG activity of the exercising forearm was measured continuously during each level of exercise and was used as an index of the level of central command. Post-exercise hyperemia was calculated as the difference between the control and the average recovery (2 min) forearm blood flows (venous occlusion plethysmography) and was examined as a possible index of the stimulus for muscle chemoreflex activation. Heart rate, arterial pressure, forearm EMG activity, and post-exercise hyperemia all increased progressively with increasing exercise intensity. The magnitudes of the increases in heart rate and arterial pressure from control to exercise were directly related to both the level of EMG activity and the degree of post-exercise hyperemia across the five exercise intensities (delta heart rate vs EMG activity: r = 0.99; delta arterial pressure vs EMG activity: r = 0.99; delta heart rate vs hyperemia: r = 0.99; and delta arterial pressure vs hyperemia: r = 0.98; all p less than 0.01). Furthermore, the level of EMG activity was directly related (r = 0.99) to the corresponding degree of hyperemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Physiological↗

PubMed1988

Endogenous digoxin-like immunoreactivity in blood is increased during prolonged strenuous exercise.

Digoxin-like immunoreactive factors (DLIFs) in serum may represent endogenous cardiotropic agents. We determined if blood levels of these endogenous factors changed during prolonged strenuous exercise. Total and loosely protein-bound (LPB) DLIF were measured by radioimmunoassay in the serum of nine healthy subjects during prolonged exercise to exhaustion. Mean total and LPB serum levels of DLIF increased by 72% (580 to 945 pg/mL) and 63% (53 to 91 pg/mL) over baseline values in digoxin equivalents (p less than 0.01), respectively, after three hours of exercise at 70% of VO2max. The prevalent serum nonesterified fatty acids (arachidonic, linoleic, oleic, palmitic, and stearic acids) as well as hydrocortisone did not account for the observed elevations in DLIF. Percent left ventricular fractional shortening (%FS) and mean velocity of left ventricular circumferential fiber shortening (mVCF) measured echocardiographically were lower (-18.0% and -16.4%, respectively, p less than 0.05) after exercise as compared to prior to exercise. Cardiac left ventricular dysfunction as measured by %FS did correlate with blood levels of DLIF (r = -0.680, p less than 0.02). These observations may suggest a relationship between serum levels of DLIF and cardiac fatigue.

Adult↗

PubMed1988

Time to fatigue during isometric exercise using different muscle masses.

The purpose of this study was to test the hypothesis that differences in the pressor response to static exercise using varying muscle masses are due to differences in endurance time. i.e., time to fatigue. Ten healthy, male subjects (mean age 24 +/- 3 years) participated in the study. With no knowledge of the purpose of the study, the subjects were instructed to maintain static contractions for as long as possible during 30% maximal voluntary contraction (MVC) in handgrip (HG), two-leg extension (LE), and dead lifting (DL). Inability to sustain a contraction within 10% of the designated force (30% MVC) marked the endurance time end point. During sustained contractions, heart rate, blood pressure, and time to fatigue were measured. Times to fatigue were 3.39 +/- 0.92, 3.61 +/- 1.67, and 3.68 +/- 1.34 min for HG, LE, and DL, respectively. These differences were not significant (p greater than 0.05). Heart rate and blood pressure increased progressively with sustained contractions, DL greater than LE greater than HG. LE and DL responses were consistently and significantly (P less than 0.05) higher than HG responses reflecting the magnitude of absolute force of contractions. The magnitude of the pressor response to the three sustained static contraction maneuvers was not related to the time to fatigue. The data affirm the view that the pressor response is a function of muscle mass activated and the absolute force developed during static exercise.

Adult↗

PubMed1988

Respiratory sinus arrhythmia and carotid baroreflex control of heart rate in endurance athletes and untrained controls.

The purpose of this study was to compare the magnitude of the respiratory sinus arrhythmia, an index of cardiac vagal tone, and carotid baroreflex control of heart rate in endurance-trained athletes (n = 12, aged 20 +/- 1 years, means +/- SE) and untrained control subjects (n = 12, aged 22 +/- 1 year). Average R-R interval (ECG) and its variability were determined at rest under controlled breathing conditions, and the changes in R-R interval in response to brief applications of suction (-10, -25, -40 mmHg) and pressure (10 and 30 mmHg) to the carotid sinus region of the neck were also measured. The average R-R interval at rest was greater in the athletes vs. controls (1150 +/- 45 vs. 854 +/- 44 ms, P less than 0.001), but the standard deviation of the R-R intervals was similar in the two groups (72 +/- 15 vs. 70 +/- 9 ms). The magnitude of the tachycardia in response to neck pressure was also similar in the athletes and controls. Although the heart rate responses to neck suction were not significantly different between the two groups, there was a strong trend for attenuated bradycardic responses in the athletes at the two highest stimulus levels (70 +/- 14 vs. 97 +/- 25 ms and 86 +/- 14 vs. 145 +/- 38 ms for the -25 and -40 mmHg levels, respectively, P greater than 0.1). The results of this study do not support the postulate that cardiac vagal tone is enhanced in the endurance-trained state.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1988

Autonomic mediation of the pressor responses to isometric exercise in humans.

The purpose of this study was to determine the respective contributions of tachycardia and increases in sympathetic nerve activity (SNA) in mediating the pressor responses to fatiguing vs. nonfatiguing levels of isometric handgrip exercise (IHE) in humans. We performed direct (microneurographic) measurements of muscle SNA from the right peroneal nerve in the leg and recorded arterial pressure (AP) and heart rate (HR) in eight healthy subjects before (control), during, and after 2.5 min of IHE at 15, 25, or 35% of maximal voluntary contraction (MVC). At 15% MVC, AP increased during the initial 1.5 min of IHE (7 mmHg, P less than 0.05) and remained at this level; at 25 and 35% MVC, AP increased throughout IHE (22 and 34 mmHg vs. control, respectively, P less than 0.05). HR increased during the initial 1.5 min of IHE at all three levels (5, 12, and 19 beats/min, respectively, P less than 0.05) but did not increase further over the last minute. At 15% MVC, muscle SNA did not increase above control; during 25 and 35% MVC, muscle SNA did not increase during the 1st min of IHE but increased progressively thereafter (109 and 205% vs. control, respectively, P less than 0.05). The magnitudes of the average increases in AP and muscle SNA over the last minute of IHE were directly related (r = 0.99, P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1988

Cardiopulmonary baroreflexes do not modulate exercise-induced sympathoexcitation.

The purpose of this study was to test the general hypothesis that sympathoinhibitory cardiopulmonary baroreflexes modulate sympathetic outflow during voluntary exercise in humans. Direct (microneurographic) measurements of postganglionic sympathetic nerve activity to noncontracting muscle (MSNA) were made from the right peroneal nerve in the leg, and arterial pressure (AP) and heart rate (HR) were recorded in 10 healthy subjects before (control) and for 2.5 min during each of five interventions: 1) lower-body negative pressure at -10 mmHg (LBNP) alone, 2 and 3) isometric handgrip exercise at 15 and 30% of maximal voluntary contraction (MVC) alone, and 4 and 5) handgrip at 15 and 30% MVC performed during LBNP. During LBNP alone, which should have reduced cardiopulmonary baroreflex sympathoinhibition, AP and HR did not change from control, but MSNA increased 93 +/- 24% (P less than 0.05). Handgrip elicited contraction intensity-dependent increases in AP and HR (P less than 0.05), but MSNA increased above control only at the 30% MVC level (165 +/- 30%, P less than 0.05). The HR, AP, and MSNA responses to either level of handgrip performed during LBNP were not different from the algebraic sums of the corresponding responses to handgrip and LBNP performed separately (P greater than 0.05). Since there was no facilitation of the MSNA response to handgrip when performed during LBNP compared with algebraic sums of the separate responses, our results do not support the hypothesis that cardiopulmonary baroreflexes modulate (inhibit) sympathetic outflow during exercise in humans.

Adult↗

PubMed1988

Pulmonary function in young and older athletes and untrained men.

This study compared the lung volumes and pulmonary functions of older endurance-trained athletes with those of healthy sedentary age-matched controls, young athletes, and young untrained men to determine whether training affects the age-associated changes in these variables. Despite large differences in maximal 02 consumption (VO2max), the older athletes and their sedentary peers had similar values for all pulmonary variables when expressed as absolute values. However, because the older athletes were shorter than the older sedentary men, their vital capacity, total lung capacity (TLC), and forced expiratory volume in 1 s were significantly larger than those of the older sedentary men when normalized for age and height; the average values for maximal voluntary ventilation and residual volume (RV) were also larger in the older athletes when normalized for age and height, but the differences were not significant. The young trained and untrained men did not differ in any of these measures. TLC was the only pulmonary variable that was the same in the young and older men; RV and the RV-to-TLC ratio were larger, whereas all other pulmonary function and volume measures were lower in the older men compared with the younger men. The older athletes were the only group whose lung volumes and pulmonary function measures were all, except for RV, substantially greater than expected based on their age and height. Thus prolonged strenuous endurance training in these older highly trained endurance athletes appears to have altered the decline in pulmonary function and volumes associated with aging.

Adult↗