Lois M. Sheldahl

Effect of head-out water immersion on cardiorespiratory response to dynamic exercise

Head-out water immersion is known to produce several cardiopulmonary adjustments at rest due to a cephalad shift in blood volume. The purpose of this study was to determine the effect of head-out water immersion on the cardiorespiratory response to graded dynamic exercise. Nineteen healthy middle-aged men performed upright cycling exercise at 40, 60 and 80% of maximal oxygen consumption on land and in water (31.0 +/- 1.0 degrees C) to the shoulders. Cardiac output (measured by the carbon dioxide rebreathing technique) was significantly greater in water at 40 and 80% maximal oxygen consumption. Stroke volume was significantly elevated at all stages of exercise. Heart rate did not differ significantly at 40 and 60% maximal oxygen consumption but was significantly lower in water at 80% maximal oxygen consumption. Total ventilation did not differ significantly in water and on land at any stage of exercise. The results suggest that the central redistribution of blood volume with head-out water immersion leads to an increase in stroke volume. Because there is not a proportional decrease in heart rate with the elevated stroke volume, cardiac output is regulated at a higher level during upright exercise in water compared with that on land. In conclusion, there are serious limitations of available, prerecorded rhythm data bases for designing and testing of automatic external defibrillators. Performance can be adequately assessed only by extensive clinical tests, which seem mandatory for this new and important type of defibrillator.

Association of Dehydroepiandrosterone Sulfate, Body Composition, and Physical Fitness in Independent Community-Dwelling Older Men and Women

OBJECTIVES: To determine the association of dehydroepiandrosterone sulfate (DHEAS), body composition, and physical fitness in independent community‐dwelling men and women aged 60 to 80 years.

Physiological comparison of walking among bilateral above-knee amputee and able-bodied subjects, and a model to account for the differences in metabolic cost

OBJECTIVE To compare the metabolic cost for prosthetic ambulation among persons with bilateral above-knee amputation with that for able-bodied ambulation, and to test a model that differentiates the metabolic cost of walking into three components. DESIGN Cross-sectional comparison. SETTING Community-dwelling subjects studied at an academic medical center. PARTICIPANTS Five bilateral above-knee amputee subjects with mean (+/-SD) age of 22 +/- 3 years, and five able-bodied control subjects matched for gender, height, weight, and age. INTERVENTION Subjects performed 6-minute bouts of walking at three paced speeds and their chosen walking speed with oxygen uptake being determined during the last 2 minutes of each bout. MAIN OUTCOME MEASURES Chosen walking speed and oxygen uptake during each walking condition. RESULTS The chosen walking speed was 21% slower and induced aerobic demands 49% higher for the amputee subjects. Across specified paced speeds, aerobic demands were 55% to 83% higher for the amputee subjects than for the able-bodied subjects. The described model suggests that the higher metabolic costs for the amputee subjects resulted from greater demands for maintenance of balance and posture and for performing the walking movement. CONCLUSIONS Prosthetic ambulation by young healthy persons with bilateral above-knee amputation induces significantly greater metabolic demands than walking by able-bodied individuals. Although the chosen walking speed of persons with bilateral above-knee amputation is slower, the reduction in speed is insufficient to equalize their metabolic cost with that of able-bodied individuals walking at their chosen walking speed.

Predictors of Lean Body Mass and Total Adipose Mass in Community-Dwelling Elderly Men and Women

As part of an ongoing longitudinal study, we analyzed cross-sectional data to identify the predictors of lean body mass (LBM) and total adipose mass (TAM) in community-dwelling elderly men and women. Body composition analysis was done using dual energy x-ray absorptiometry. A total 262 subjects (118 women and 144 men), 60 to 80 years of age, from the urban and suburban communities of southeastern Wisconsin were studied. In women, the age (r = -.18), body mass index (BMI) (r = .43), and waist-to-hip ratio (WHR) (r = .30), and in men, BMI (r = .45) and insulin-like growth factor-1 (IGF-1) (r = .32) were identified as predictors (P < .05) of LBM. In women, the BMI (r = .87), WHR (r = .21), and functional work capacity (VO2 max) (r = -.47), and in men, the BMI (r = .83), WHR (r = .52), dehydroepiandrosterone sulfate (DHEAS) (r = -.27), total testosterone (TT) (r = -.35), free testosterone (FT) (r = -.23), physical activity (LTE) (r = -.32), and VO2 peak (r = -.59) were identified as predictors of TAM. After partialling out age in addition to the predictors identified earlier, the VO2 peak was identified as a predictor (P < .05) of LBM in both women and men, and TT, FT, and LTE as predictors (P < .05) of LBM in men. We conclude that the BMI, WHR, and VO2 peak influences LBM and TAM in both women and men. Additionally, in men LBM and TAM is influenced by hormone profile.

Response of patients after myocardial infarction to carrying a graded series of weight loads

Cardiovascular responses to carrying graded weight loads of 20 to 50 pounds were determined in 52 patients after myocardial infarction (MI) (greater than or equal to 2 months). Sixty percent of the patients were stopped before completing the heaviest weight load (50 pounds for 2 minutes) because of an increase in diastolic blood pressure (BP) to 120 mm Hg (end point) or arm fatigue. Compared with symptom-limited graded dynamic exercise, peak systolic and diastolic BP were significantly greater (p less than 0.05 and p less than 0.01, respectively) with weight carrying, while peak heart rate, pressure-rate product, ventilation and oxygen consumption were significantly lower (p less than 0.01). Ischemic responses were less frequent with weight carrying. Patients with severely reduced resting left ventricular ejection fraction (LVEF) (less than 35%) tolerated the weight carrying test as well as patients with normal resting LVEFs (greater than 50%). We conclude that (1) ischemic responses occur less frequently while carrying up to 50 pounds for 2 minutes than with symptom-limited dynamic exercise, (2) a significant number of patients have an increase in diastolic BP greater than or equal to 120 mm Hg while carrying objects that weigh 30 to 50 pounds for 2 minutes, and (3) a poor correlation exists between resting LVEF and tolerance for weight carrying.

Energy expenditure during household tasks in women with coronary artery disease

The energy expenditure for and heart rate responses to common household tasks were determined in 26 older (mean age 62 +/- 2 years) women with coronary artery disease (CAD). Each activity was performed at a self-determined pace for 6 or 8 minutes. The average oxygen uptake (ml/kg/min) for each task evaluated was 6.5 for washing dishes, 6.8 for ironing, 7.2 for scrubbing pans, 8.6 for unpacking groceries, 9.5 for vacuuming, 9.8 for sweeping, 10.1 for mopping, 12.0 for changing bed linens, and 12.4 for washing the floor (hands and knees). None of the subjects reported angina. Mean relative oxygen uptake (i.e., percentage of peak response with treadmill testing) ranged from 31 +/- 2% for washing dishes to 62 +/- 3% for changing the bed linens and washing the floor. Percentage of peak treadmill heart rate ranged from 62 +/- 2% for washing dishes to 73 +/- 2% for washing the floor. In 4 of the more physically demanding household activities (i.e., vacuuming, mopping, washing the floor, and changing bed linens), the responses of 10 age-matched normal women were evaluated. The absolute and relative demands of the tasks were similar between the CAD and normal groups. Results indicate that the mean energy expenditure rate of common household tasks evaluated in this study range from 2 to 4 METs, suggesting that most women with CAD who are able to achieve > or = 5 METs during a treadmill exercise test without adverse signs or symptoms should be able to resume these activities.

Effect of age and coronary artery disease on response to snow shoveling.

Objectives. The objective of this study was to evaluate the effect of age and coronary artery disease on responses to snow shoveling. Background. Little information is available on the hemodynamic and metabolic responses to snow shoveling. Methods. Sixteen men with asymptomatic coronary artery disease and relatively good functional work capacity, 13 older normal men and 12 younger normal men shoveled snow at a self-paced rate. Oxygen consumption, heart rate and blood pressure were determined. In nine men with coronary artery disease left ventricular ejection fraction was evaluated with an ambulatory radionucilde recorder. Results. Oxygen consumption during snow shoveling differed (p < 0.05) among groups; it was lowest (18.5 ± 0.8 ml/kg per min) in those with coronary artery disease, intermediate (22.2 ± 0.9 ml/kg/min) in older normal men and highest (25.6 ± 1.3 ml/kg/min) in younger normal men. Percent peak treadmill oxygen consumption and heart rate with shoveling in the three groups ranged from 60% to 68% and 75% to 78%, respectively. Left ventricular ejection fraction and frequency of arrhythmias during shoveling were similar to those during treadmill testing. Conclusions. During snow shoveling 1) the rate of energy expenditure selected varied in relation to each mans peak oxygen consumption; 2) older and younger normal men and asymptomatic men with coronary artery disease paced themselves at similar relative work intensities; 3) the work intensity selected represented hard work but was within commonly recommended criteria for aerobic exercise training; and 4) arrhythmias and left ventricular ejection fraction were similar to those associated with dynamic exercise.

Effect of enhanced preload with head-out water immersion on exercise response in men with healed myocardial infarction.

Head-out water immersion shifts venous blood to the central vasculature and heart and subsequently increases cardiac preload. In healthy men, cardiac output and stroke volume are greater during upright leg cycle exercise in water than on land. Heart rate is similar during work loads < 50% of peak oxygen consumption but is decreased in water at higher work intensities. To determine if men with myocardial infarction (MI) show a similar response, 15 men with a documented MI exercised upright on a leg cycle ergometer on land and immersed in water (31 +/- 1 degree C) to the level of the shoulders. Heart rate, cardiac output (carbon dioxide rebreathing procedure) and oxygen consumption were measured at rest and at work loads corresponding to approximately 40, 60 and 75% of peak oxygen consumption in both environments. At rest, cardiac output and stroke volume were elevated (p < 0.05) in water. During exercise, heart rate, cardiac output and stroke volume did not differ between water and land. When subjects were given beta-blocking medications (n = 8) and subjects with exercise-induced ST-segment depression (n = 5) were separately excluded from the analysis, water immersion still did not significantly change exercise responses. These results suggest that MI alters the normal cardiac response to increased preload during exercise. The alteration may involve reduced myocardial compliance or near-complete use of the Frank-Starling reserve, or both, during land exercise.

Comparison of adaptations and compliance to exercise training between middle-aged and older men.

Objective: To compare the rate and magnitude of physiologic and psychologic adaptations to aerobic training between middle‐age and older men, to assess their interest in continued participation (>6 months) in a supervised high‐intensity training program, and to evaluate the safety of high‐intensity training for older people.

The safety of static-dynamic effort soon after myocardial infarction

Many activities of daily living require static-dynamic effort. To evaluate the safety of such effort 3 weeks after myocardial infarction, 27 male patients underwent a weight-carrying test requiring 5 minutes of treadmill ambulation with graded weight loads of 10 to 30 pounds. The hemodynamic responses with weight carrying were compared to that of a predischarge graded dynamic exercise test. The peak heart rate was significantly lower (p less than 0.01) with weight carrying, the peak systolic blood pressure did not differ, and the diastolic pressure was significantly higher (P less than 0.01). ST segment depression and angina pectoris occurred less frequently with weight carrying. The type and frequency of ventricular arrhythmias were similar between the two tests. We conclude that many men are capable of performing static-dynamic activity equivalent to carrying up to 30 pounds by 3 weeks after myocardial infarction.