E. R. Nadel

A survey for assessing physical activity among older adults.

In 1988, the Yale Physical Activity Survey (YPAS) was designed and then administered to healthy older populations of volunteers (aged 60-86) to establish its 2-wk repeatability and relative validity. Among the 76 volunteers in the repeatability substudy, correlation coefficients between the two administrations of the survey for the eight YPAS summary indices ranged from 0.42 (P = 0.0002) to 0.65 (P = 0.0001). Among the 25 subjects in the validation substudy, weekly energy expenditure (r = -0.47; P = 0.01) and daily hours spent sitting (r = 0.53; P = 0.01) correlated with resting diastolic blood pressure, while the YPAS activity dimensions summary index (composed of questions on vigorous activity, leisurely walking, moving, sitting, and standing) correlated positively with estimated VO2max (r = 0.58; P = 0.004) and inversely with percent body fat (r = -0.43; P = 0.03). The YPAS index of vigorous activity also correlated positively with estimated VO2max (r = 0.60; P = 0.003) and the moving index correlated marginally with body mass index (r = -0.37; P = 0.06). We conclude that the YPAS demonstrates adequate repeatability, and some validity by correlating with several physiologic variables reflecting habitual physical activity. The value of the YPAS, however, in accurately assessing low intensity activity remains to be established.

Differential thermal sensitivity in the human skin

SummaryThermal irradiation was applied to selected skin areas to determine whether particular areas demonstrate a greater thermal sensitivity than others in determination of a physiological thermoregulatory response. Modifications in thigh sweating rate were related to the change in temperature of the irradiated skin and the area of skin irradiated by computing a sensitivity coefficient for each skin area. Thermal sensitivity of the face, as measured by its effect on sweating rate change from the thigh, was found to be approximately three times that of the chest, abdomen men and thigh. Lower legs were found to have about one-half the thermal sensitivity of the thigh. A table of weighting factors for calculation of physiological mean skin temperature, based upon thermal sensitivity and area, is presented.

Role of changes in insulin and glucagon in glucose homeostasis in exercise.

This experiment was performed to determine if plasma glucose homeostasis is maintained in normal human volunteers during light exercise (40% maximal oxygen consumption [VO2 max]) when changes in insulin and glucagon are prevented. Hormonal control was achieved by the infusion of somatostatin, insulin, and glucagon. Glucose kinetics and oxidation rates were determined with stable isotopic tracers of glucose, and by indirect calorimetry. Two different rates of replacement of insulin and glucagon were used; in one group, insulin was clamped at 19.8 +/- 2.6 microU/ml (high-insulin group), and in the other group insulin was clamped at 9.2 +/- 1.3 microU/ml (low-insulin group). Glucagon was maintained at 261 +/- 16.2 and 124 +/- 6.4 pg/ml, respectively, in the high-insulin and low-insulin groups. Without hormonal control, plasma glucose homeostasis was maintained during exercise because the increase in glucose uptake was balanced by a corresponding increase in glucose production. When changes in insulin and glucagon were prevented, plasma glucose concentration fell, particularly in the high-insulin group. Glucose uptake increased to a greater extent than when hormones were not controlled, and glucose production did not increase sufficiently to compensate. The increase in glucose uptake in the hormonal control groups was associated with an increased rate of glucose oxidation. When euglycemia was maintained by glucose infusion in the hormonal control subjects, the modest increase in glucose production that otherwise occurred was prevented. It is concluded that during light exercise there must be a reduction in insulin concentration and/or an increase in glucagon concentration if plasma glucose homeostasis is to be maintained. If such changes do not occur, hypoglycemia, and hence exhaustion, may occur.

Estrogen influences osmotic secretion of AVP and body water balance in postmenopausal women

To determine if estrogen upregulates osmotic secretion of arginine vasopressin (AVP) and alters body water balance, we infused hypertonic (3% NaCl) saline in 6 women (68 ± 3 yr) after 14 days of 17β-estradiol (transdermal patch, ∼0.1 mg/day, E2) and placebo (control) administration. Hypertonic saline was infused at 0.1 ml ⋅ kg-1 ⋅ min-1for 120 min, and after a 30-min equilibration period, the subjects drank water ad libitum for 180 min. E2 increased basal plasma estradiol concentration from ≤12 to 80 ± 12 pg/ml and plasma AVP concentration (P[AVP]) from 2.1 ± 0.7 to 3.1 ± 0.8 pg/ml ( P< 0.05), but not plasma osmolality (Posm, 288 ± 1 and 287 ± 1, for control and E2, respectively). Hypertonic saline infusion increased Posm by 18 ± 1 and 17 ± 1 mosmol/kgH2O and P[AVP] by 5.2 ± 0.5 and 4.9 ± 0.4 pg/ml for control and E2 treatments, respectively. The P[AVP]-Posmrelationship shifted upward after E2, with no change in sensitivity (slope, 0.36 ± 0.02 and 0.33 ± 0.03 pg ⋅ ml-1 ⋅ mosmol-1for control and E2, respectively). Water intake was similar between control and E2 (24 vs. 22 ml/kg), but by 180 min of drinking, urine output and free water clearance ([Formula: see text]) were reduced by 5.6 ± 2.3 ml/kg and 2.6 ± 2.0 ml/min, respectively ( P < 0.05) after E2. Plasma aldosterone concentration was unaffected by E2, but fractional sodium excretion was reduced from 2.7 ± 0.5 to 1.7 ± 0.4% ( P < 0.05) at 180 min of drinking. Our data suggest that E2augments osmotic AVP secretion, thereby implicating elevated AVP as a contributor to water retention in high E2 states; however, an increase in renal sodium reabsorption was a major component of the enhanced fluid retention.

Moderate-intensity aerobic training improves glucose tolerance in aging independent of abdominal adiposity.

OBJECTIVE: To test the hypothesis that training‐related improvements in glucose and insulin responses to an oral glucose tolerance test (OGTT) are independent of changes in abdominal adiposity.

Diminished Baroreflex Control of Forearm Vascular Resistance Following Training

The stimulus-response characteristics of cardiopulmonary baroreflex control of forearm vascular resistance (FVR units in mm Hg.min.100 ml.ml-1) were studied in 14 volunteers before and after 10 wk of endurance training. We assessed the relationship between reflex stimulus (changes in central venous pressure, CVP) and response (FVR) during unloading of cardiopulmonary baroreceptors with lower body negative pressure (LBNP, 0 to -20 mm Hg). Changes in CVP during LBNP were estimated from pressure changes in a large peripheral vein in the dependent arm of the subject in the right lateral decubitus position. Maximal oxygen uptake (VO2max) and total blood volume increased with endurance training from 37.8 +/- 1.4 ml.min-1.kg-1 and 63.6 +/- 2.1 ml.kg-1 to 45.3 +/- 1.4 ml.min-1.kg-1 and 69.3 +/- 2.8 ml.kg-1, respectively (P less than 0.05). Reflex forearm vasoconstriction occurred in response to a reduction in estimated CVP, and the absolute change in FVR per unit of CVP was reduced from -5.96 +/- 0.79 to -4.06 +/- 0.52 units.mm Hg-1 (P less than 0.05) following exercise training but was unchanged from -6.10 to 0.57 to -6.22 +/- 0.94 units.mm Hg-1 for the time control group (N = 7). Resting values for FVR were similar before and after exercise training; however, resting estimated CVP was elevated from 9.5 +/- 0.5 mm Hg before training to 11.3 +/- 0.6 mm Hg after training.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of blood volume during training in post-menopausal women

UNLABELLED In younger people the increase in aerobic capacity following training is related, in part, to blood volume (BV) expansion and the consequent improvements in maximal cardiac output. This training-induced hypervolemia is associated with a decrease in cardiopulmonary baroreflex (CPBR) control of peripheral vascular tone. PURPOSE To test the hypothesis that improvement in peak oxygen consumption (VO2peak) during training in older women is associated with specific central adaptations, such as BV expansion and a reduction in CPBR control of vascular tone. METHODS Seventeen healthy older women were randomized into training (N = 9, 71 +/- 2 yr) and control (N = 8, 73 +/- 3 yr) groups. The training group exercised three to four times per wk for 30 min at 60% peak heart rate for 12 wk and then 40-50 min at 75% peak heart rate for 12 wk. The control group participated in yoga exercises over the same time period. We measured resting BV (Evans blue dye), VO2peak, and the forearm vascular resistance response to unloading low pressure mechanoreceptors during low levels of lower body negative pressure (through -20 mm Hg) before and after aerobic training. The slope of the increase in forearm vascular resistance (response) per unit decrease in central venous pressure (stimulus) was used to assess CPBR responsiveness. RESULTS Aerobic training increased VO2peak 14.2% from 24.2 mL x kg(-1) x min(-1) to 27.7 mL x kg(-1) x min(-1) (P < 0.05), a smaller improvement than typically seen in younger subjects. Blood volume (59.9 +/- 1.9 and 60.9 +/- 1.9 mL x kg[-1]) and CPBR function (-3.98 +/- 0.92 and -3.46 +/- 0.94 units x mm(-1) Hg) were similar before and after training. CONCLUSIONS These data indicate that the inability to induce adaptations in CPBR function may limit BV expansion during training in older women. In addition, the absence of these specific adaptations may contribute to the relatively poor improvements in VO2peak in older women during short (10-12 wk) periods of training.

Effect of plasma volume on thermoregulation in the dog

Panting thresholds, plasma volume (PV) changes and cardiac filling pressure were studied during thermal dehydration in control, water deprived (WD) and hypovolemic (PEG) dogs. WD and PEG dogs showed a delayed panting threshold, apparently due to hypovolevoia. Initiation of heat stress however resulted in a transient plasma expansion in all dogs. Cardiac filling pressure did not change.

Effect of exercise training on cardiopulmonary baroreflex control of forearm vascular resistance in humans

We studied the stimulus-response characteristics of cardiopulmonary baroreflex control of forearm vascular resistance (FVR) in four groups of male volunteer subjects: i) unfit, ii) physically fit, iii) before and after 10 wk of endurance training (chronic blood volume expansion), and iv) before and after acute blood volume expansion. We assessed the relationship between reflex stimulus, i.e., changes in central venous pressure and response, i.e., FVR, during unloading of cardiopulmonary mechanoreceptors with lower body negative pressure (LBNP, 0 to -20 mm Hg). The slope of the linear relationship between FVR and CVP, the index of the responsiveness of this baroreflex, was significantly diminished (> 50%) in the fit subjects compared with the unfit. The slope of the FVR-CVP relationship was inversely correlated with the subjects total blood volume, suggesting that blood volume expansion was related to the attenuated CP baroreflex. In the exercise training study, maximal oxygen consumption and blood volume increased following 10 wk of endurance training (N = 14) but were unchanged in the time control group (N = 7). The slope of the FVR-CVP relationship was significantly reduced (32%) following 10 wk of training but was unchanged in the time control group. The reduction in slope of the FVR-CVP relationship was inversely related to the increase in blood volume associated with exercise training. Acute blood volume expansion 8 ml.kg-1 body weight with 5% human serum albumin solution) significantly reduced the slope of the FVR-CVP relationship. These data support the hypothesis that the attenuated forearm vascular reflex in physically fit individuals is related to a training-induced hypervolemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Factors affecting the regulation of body temperature during exercise

Abstract 1. 1.|During exercise, the heat produced in the contracting muscles causes internal body temperature to rise until the heat-dissipation responses, increasingly driven by the rising temperature, provide for a new balance between heat-production and heat-loss rates. 2. 2.|The new elevated steady-state internal body temperature is not invariant, but can be affected by a number of factors, such as wetness of the skin or state of body hydration. 3. 3.|Progressive dehydration, such as occurs during prolonged exercise or exercise in the heat, results in relative hyperthermia caused by increased thresholds and decreased sensitivities of the heat-dissipation mechanisms. Independent manipulations of blood volume and osmolality reveal that these variables exert their effects on the thermoregulatory system by somewhat different means.