Biomedical subjects

D R Pendergast

Publications and source records attributed to D R Pendergast.

At least 37 records · Page 2Linked to original sources

PubMed1997

Effect of gravity on lung exhaled nitric oxide at rest and during exercise.

Exhaled nitric oxide (NO) from the lungs (VNO) in nose-clipped subjects increases during exercise. This may be due to endothelial shear stress secondary to changes in pulmonary blood flow. We measured VNO after modifying pulmonary blood flow with head-out water immersion (WI) or increased gravity (2 Gz) at rest and during exercise. Ten sedentary males were studied during exercise performed in air and WI. Nine subjects were studied at 1 and 2 Gz. Resting NO concentrations in exhaled air ([NO]) were 16.3 +/- 8.2 ppb (air). 15 +/- 8.2 ppb (WI) and 17.4 +/- 5 ppb (2 Gz). VNO (ppb/min) was calculated as [NO]VE and was unchanged at rest by either WI or 2 Gz. VNO increased linearly with Vo2, VE and fii during exercise in air, WI and at 2 Gz. These relationships did not differ among the experimental conditions. Therefore, changes in pulmonary blood flow failed to alter the output of NO exhaled from the lungs at rest or during exercise.

Adult↗

PubMed1997

Muscle function and gait in patients with knee osteoarthritis before and after muscle rehabilitation.

Patients with knee osteoarthritis (OA) have reduced functional capacity and muscle function that improves significantly after quantitative progressive exercise rehabilitation (QPER). The effects of these changes on the biomechanics of walking have not been quantified. Our goal was to quantify the effects of knee OA on gait before and after QPER. Bilateral kinematic and kinetic analyses were performed using a standard link-segment analysis on seven women (60.9 +/- 9.4 years) with knee OA. All functional capacity, muscle function and gait variables were initially reduced compared to age-matched controls. Muscle strength, endurance and contraction speed were significantly improved (55%, 42% and 34%, respectively) after 2 months of QPER (p < 0.05), as were function (13%), walking time (21%), difficulty (33%) and pain (13%). There were no significant changes in the gait variables after QPER. To use the QPER improvements to the best advantage, gait retraining may be necessary to "re-programme' the locomotor pattern.

Aged↗

PubMed1997

Reduced muscle function in patients with osteoarthritis.

The purpose of this study was to determine whether subjects with knee osteoarthritis (OA) had reduced muscle strength at various muscle lengths, endurance, contraction velocity and functional capacity, compared with control subjects and whether the decrease was related to functional capacity. Forty-five men and 45 women with knee OA were compared with a control group (41 males, 63 females) of similar age for functional capacity, maximal isometric strength (in vivo length-tension relationship) and endurance (in vivo force-time relationship) of knee flexion and extension and maximal angular velocity (in vivo force-velocity relationship) of knee extension. The OA subjects had increased difficulty (2.03 +/- 0.53) and pain (1.65 +/- 0.29) for activities of daily living (ADLs) and significantly lower strength for extension (72%) and flexion (56%), endurance for the quadriceps (203%) and hamstrings (214%) and velocity (128%). The reductions were greater at longer muscle lengths. These data demonstrate that patients with knee OA have reduced muscle function and functional capacity compared to controls.

Aged↗

PubMed1996

Effect of the underwater torque on the energy cost, drag and efficiency of front crawl swimming.

Underwater torque (T') is defined as the product of the force with which the swimmer's feet tend to sink times the distance between the feet and the centre of volume of the lungs. It has previously been shown that experimental changes of T', obtained by securing around the swimmer's waist a plastic tube filled, on different occasions, with air, water or 2-kg lead, were accompanied by changes in the energy cost of swimming per unit of distance (Cs) at any given speed. The aim of this study was to investigate whether the observed increases of Cs with T' during front crawl swimming were due to an increase of active body drag (Db), a decrease of drag efficiency (eta /d) or both. The effect of experimental changes of T' on Cs, Db and eta /d were therefore studied on a group of eight male elite swimmers at two submaximal speeds (1.00 and 1.23 m.s-1). To compare different subjects and different speeds, the individual data for Cs, Db, eta /d and T' were normalized dividing them by the corresponding individual averages. These were calculated from all individual data (of Cs, Db, eta /d and T') obtained from that subject at that speed. It was found that, between the two extremes of this study (tube filled with air and with 2-kg lead), T' increased by 73% and that Cs, Db and eta /d increased linearly with T'. The increase of Cs between the two extremes was intermediate (approximately 20%) between that of Db (approximately 35%) and of eta /d (approximately 16%). Thus, the actual strategy implemented by the swimmers to counteract T', was to tolerate a large increase of Db. This led also to a substantial (albeit smaller) increase of r/d, the effect of which was to reduce the increase of Cs that would otherwise have occurred.

Adult↗

PubMed1996

Energetics of underwater swimming with SCUBA.

Underwater swimming has unique features of breathing apparatus (SCUBA), thermal protective gear, and fins. The energy cost of underwater swimming is determined by the drag while swimming and the net mechanical efficiency. These are influenced by the cross-sectional area of the diver and gear and the frequency of the leg kick. The speeds that divers can achieve are relatively low, thus the VO(2) increases linearly with values of VO(2)*d(-1) of 30-50 l*km(-1)for women and men, respectively. Diving experience had little effect on VO(2) for women; however, male divers with experience had lower VO(2) than beginners. The location and density of the gear can alter the diver's attitude in the water and increase the energy cost of swimming by 30 percent at slow speeds. The type of fin used has an effect on the depth and frequency of the kick, thus on drag and efficiency, with a range of VO(2) from 25 to 50 l*km(-1). A large flexible fin had the lowest energy cost and a large rigid fin the highest. Adding extra air tanks or a dry suit increased the cost of swimming by 25 percent. The energy cost of underwater swimming is influenced by gender, gear and its placement, fin type, and experience of the diver.

Diving↗

PubMed1996

Effects of body size, body density, gender and growth on underwater torque.

Two forces act on a human body motionless in water: weight (W) and buoyancy (B). They are applied to the center of mass (CM) and to the center of volume (CV) of the subject, respectively. CM and CV do not coincide; this generates a torque that is a measure of the tendency of the upper part of the body to rise, rotating around its center of mass. To quantify this tendency, Pendergast & Craig defined 'underwater torque' (T') as the product of the net force with which the feet of a subject lying horizontally in water tend to sink, times the distance between the feet and the center of volume of the lungs. In this paper we have investigated: (a) the relationships between T' and body weight (BW), height (H), body surface area (BS), body density (BD) and leg density (LD) in a group of 30 subjects (group A, 14 females and 16 males, age range 16-50 years); and (b) the effect of gender and growth on T' in a group of 110 subjects (group B, 67 girls and 43 boys, age range 12-17 years). In group A, T' was found to be linearly related with BW (r=0.833, P<0.001), H (r=0.803, P<0.001), BS (r=0.866, P<0.001), BD (r=0.617, P<0.001) and LD (r=0.549, P<0.005). A multiple linear regression analysis showed that BS and BD explained about 85% of the variability of T' (r2=0.85). In group B, T' was found to increase linearly with age (r=0.47, P<0.01), the increasing rate being three times higher in boys compared with girls. As a consequence, the T' ratio between boys and girls increased with age, from 1.69 at 13 years to 2.04 at 16 years.

Adolescent↗

PubMed1996

Cardiovascular response to submaximal exercise in sustained microgravity.

Cardiac output (Q), heart rate (HR), blood pressure, and oxygen consumption (VO2) were measured repeatedly both at rest and at two levels of exercise in six subjects during microgravity exposure. Exercise was at 30 and 60% of the workload producing the individual's maximal VO2 in 1 G. Three of the subjects were on a 9-day flight, Spacelab Life Sciences-1, and three were on a 15-day flight, Spacelab Life Sciences-2. We found no temporal differences during the flights. Thus we have combined all microgravity measurements to compare in-flight values with erect or supine control values. At rest, Q in flight was 126% of Q erect (P < 0.01) but was not different from Q supine, and HR in flight was 81% of HR erect (P < 0.01) and 91% of HR supine (P < 0.05). Thus resting stroke volume (SV) in flight was 155% of SV erect (P < 0.01) and 109% SV supine (P < 0.05). Resting mean arterial blood pressure and diastolic pressure were lower in flight than erect (P < 0.05). Exercise values were considered as functions of VO2. The increase in Q with VO2 in flight was less than that at 1 G (slope 3.5 vs. 6.1 x min-1.l-1.min-1). SV in flight fell with increasing VO2, whereas SV erect rose and SV supine remained constant. The blood pressure response to exercise was not different in flight from erect or supine. We conclude that true microgravity causes a cardiovascular response different from that seen during any of its putative simulations.

Adult↗

PubMed1996

The role of dietary fat on performance, metabolism, and health.

This paper presents a model to evaluate the nutritional status of trained athletes based on work in our laboratory as well as others. The model proposes that substrate use is set by the muscle fibers recruited, based on the exercise intensity. Second, the substrate available is primarily determined by the intramuscular stores. In trained athletes, intramuscular fat plays an important role in metabolism at exercise intensities as high as 80% of maximal aerobic power. Based on these factors, increasing the fat in the diet (while maintaining adequate intramuscular glycogen) increases VO2max and intramuscular stores of fat (presumably due to increased mitochondrial volume). These two factors result in a significant increase in the time to exhaustion at set levels of exercise (endurance). It also appears that fatigue is associated with depletion of either glycogen or fat. These conclusions hold true for athletes on diets where sufficient calories are taken in to meet demands and for exercise levels below 80% of VO2max, where primarily slow-twitch oxidative fibers are used. These data may not apply in exercise where predominantly fast-twitch fibers are used. Also, these data do not apply to runners eating a hypocaloric diet, where reducing the percentage of carbohydrates may compromise their glycogen stores. It would appear that the fat in the diet can be increased to a very high level without compromising the cardiovascular or immune systems of athletes. Moreover, it can be proposed that these data could be applied to sedentary persons, as long as they are isocaloric. This would imply that the fat consumed in the diet would be used in the muscle, as in the runners, although at a lower level. Thus, the dietary intake should be matched in both total calories and percentage of fats and carbohydrates to calories consumed by daily activity. It should be cautioned that if glycogen and fat stores are compromised, protein resynthesis is inhibited and loss of muscle mass may result. This has a negative effect on the athlete's ability to perform at high levels.

Anaerobiosis↗

PubMed1995

Bioenergetics and biomechanics of front crawl swimming.

"Underwater torque" (T') is one of the main factors determining the energy cost of front crawl swimming per unit distance (Cs). In turn, T' is defined as the product of the force with which the swimmer's feet tend to sink times the distance between the feet and the center of volume of the lungs. The dependency of Cs on T' was further investigated by determining Cs in a group of 10 recreational swimmers (G1: 4 women and 6 men) and in a group of 8 male elite swimmers (G2) after T' was experimentally modified. This was achieved by securing around the swimmers' waist a plastic tube filled, on different occasions, with air, water, or 1 or 2 kg of lead. Thus, T' was either decreased, unchanged, or increased compared with the natural condition (tube filled with water). Cs was determined, for each T' configuration, at 0.7 m/s for G1 and at 1.0 and 1.2 m/s for G2. For T' equal to the natural value, Cs (in kJ.m-1.m body surface area-2) was 0.36 +/- 0.09 and 0.53 +/- 0.13 for G1 in women and men, respectively, and 0.45 +/- 0.05 and 0.53 +/- 0.06 for G2 at 1.0 and 1.2 m/s, respectively. In a given subject at a given speed, Cs and T' were linearly correlated. To compare different subjects and different speeds, the single values of Cs and T' were normalized by dividing them by the corresponding individual averages. These were calculated from all single values (of Cs or T') obtained from that subject at that speed.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1995

Effects of short-term and prolonged immersion on the cardiovascular responses to exercise.

The primary purpose of this investigation was to examine the effects of water immersion in 35 degrees C water, per se, and the effects of 3 h of water immersion on the physiological responses to exercise. Experiments in air were conducted after 15 min of water immersion and after 3 h of water immersion. After each condition, exercises of 20%, 40%, 60%, 80%, and 100% of the subject's maximum oxygen consumption were performed on a cycle ergometer. Oxygen consumption (VO2), cardiac output, heart rate (HR), stroke volume, and blood pressure were determined. At submaximal workloads, no significant differences in the data were observed. The VO2 at the maximal workload after 3 h of immersion (3.32 +/- 0.15 L.min-1) was significantly higher than the value after 15 min of immersion (3.03 +/- 0.20 L.min-1). Both of these values were significantly lower than the value in air (3.83 +/- 0.30 L.min-1). The peak HR's were significantly higher after 3 h of immersion (167 +/- 2 b.min-1). These observations suggest that 3 h of immersion can cause alterations in the cardiovascular responses to maximal exercise; however, submaximal responses were unaffected.

Adult↗

PubMed1994

Effect of graded exercise on nitric oxide in expired air in humans.

This study was performed to determine the influence of graded dynamic exercise and of voluntary hyperventilation on both the concentration ([NO]) and the amount of nitric oxide per unit time (VNO) in exhaled air. Young human subjects (n = 8) of varying fitness levels having peak O2 consumption (VO2) values ranging between 25.7 and 50.9 ml/min/kg were studied during graded levels of treadmill exercise. Expired [NO] determined by chemiluminescence was 26.3 +/- 6.7 SE parts per billion (ppb) at rest ranging between 11 and 66 ppb. Although variable, [NO] was maintained as work rate increased. VNO rose significantly in most subjects from a mean resting value of 12.3 +/- 3.5 nmol/min. VNO correlated linearly and significantly with ventilation (VE) and CO2 output in 6 of 8 subjects, with VO2 in 4 of 8 subjects, and with heart rate in 5 of 8 subjects. Increases of VNO per unit increase of VE were significantly higher in subjects having higher peak VO2 levels. Voluntary hyperventilation (two-fold of the control VE) for 1 min in 6 subjects decreased expired [NO] from 9.5 (+/- 2.5) to 4.8 (+/- 2.8) ppb and VNO was unchanged, while hyperventilation at 3 x control VE increased VNO by 50% and [NO] decreased to 4.7 +/- 1.8 ppb. VNO appeared to be related to VO2 during hyperventilation. The results suggest that VNO can be correlated with ventilation and heart rate during exercise and with VO2 during both exercise and hyperventilation. [NO] is influenced by the flow rate of the expired air whereas VNO is influenced by NO clearance at the alveolus.

Adult↗

PubMed1994

Cardiorespiratory response to lower body negative pressure.

The cardiovascular effects of supine lower body negative pressure (LBNP, 0 mm Hg, -8 mm Hg, -15 mm Hg, -25 mm Hg, -35 mm Hg, and -45 mm Hg) were studied in humans (n = 10). The LBNP's were applied in a random order (three per session) for 20 min, with 15 min between each LBNP. Leg blood flow, cardiac output (Q), stroke volume (SV) and estimated lung blood volume were significantly reduced at -15 mm Hg. Increasing LBNP to -35 mm Hg did not result in further changes. When the LBNP was increased to -45 mm Hg, Q and SV were lower than comparable values at -15 mm Hg. Heart rate was unchanged up to -25 mm Hg, after which it increased proportionally to the LBNP. Systolic blood pressure was maintained throughout. Diastolic blood pressure was unchanged below -45 mm Hg, but was significantly elevated at -45 mm Hg. Mean arterial pressure was maintained up to LBNP's of -35 mm Hg by increased vascular resistance, in spite of reduced thoracic blood volume, as indicated by reduced central venous pressure and Q. Greater levels of LBNP were outside the physiological adjustment range and blood pressure dropped progressively.

Adult↗

PubMed1994

Effects of a muscle exercise program on exercise capacity in subjects with osteoarthritis.

Maximal aerobic power and muscle function have been shown to decrease with age and to be even lower in patients with osteoarthritis (OA). This study was designed to determine if subjects with OA who underwent only a muscle exercise program had improved exercise capacity and cardiovascular fitness. A maximal graded exercise test was given before and after 3 months of exercise (isometric, isotonic, and isometric force generated as a function of time contractions, three times a week). Maximal strength and the tension-time index improved significantly. Peak aerobic power increased from 15.99 +/- 3.96 mL.kg-1.min-1 to 20.34 +/- 3.29 mL.kg-1.min-1. On average, maximal walking speed increased from 2.0 +/- 0.6 mph to 2.4 +/- 0.7mph. Exercise time increased 22%, from 9.2 +/- 2.3 minutes to 11.2 +/- 2.7 minutes. There were significant reductions in submaximal heart rate (15b.min-1) and systolic blood pressure (15mmHg) after training. It would appear that the reduction in aerobic fitness of subjects with OA is secondary to their reduced muscle function. By improving muscle function, increases in exercise capacity and aerobic fitness occurred.

Aged↗

PubMed1994

Effect of dietary fat on metabolic adjustments to maximal VO2 and endurance in runners.

The present study examined the effects of dietary manipulations on six trained runners. The percent energy contributions from carbohydrate, fat, and protein were 61/24/14, 50/38/12, and 73/15/12 for the normal (N), fat (F), and carbohydrate (C) diets, respectively. Expiratory gases and blood responses to a maximum (VO2max) and a prolonged treadmill run were determined following 7 d on each diet. Free fatty acids (FFA), triglycerides, glycerol, glucose, and lactate were measured. Dietary assessment of subjects' N diet indicated that they were consuming approximately 700 kcal.d-1 less than estimated daily expenditures. Running time to exhaustion was greatest after the F diet (91.2 +/- 9.5 min, P < 0.05) as compared with the C (75.8 +/- 7.6 min, P < 0.05) and N (69.3 +/- 7.2 min, P < 0.05) diets. VO2max was also higher on the F diet (66.4 +/- 2.7 ml.kg-1 x min-1, P < 0.05) as compared with the C (59.6 +/- 2.8 ml.kg-1 x min-1, P < 0.05) and N (63.7 +/- 2.6 ml.kg-1 x min-1, P < 0.05) diets. Plasma FFA levels were higher (P < 0.05) and glycerol levels were lower (P < 0.05) during the F diet than during the C and N diets. Other biochemical measures did not differ significantly among diets. These data suggest that increased availability of FFA, consequent to the F diet, may provide for enhanced oxidative potential as evidenced by an increase in VO2max and running time. This implies that restriction of dietary fat may be detrimental to endurance performance.

Analysis of Variance↗

PubMed1993

Quantitative effects of physical therapy on muscular and functional performance in subjects with osteoarthritis of the knees.

Osteoarthritis (OA) of the knees is a functionally limiting disability. Physical therapy (PT) is considered a useful treatment for OA, although evidence is qualitative. The purpose of this study was to quantitatively measure the effects of a 3-month PT program (n = 40; 20 men and 20 women) with knee OA. Muscle function and functional assessment parameters were measured. All data were analyzed by repeated measures analysis of variance (p < 0.05). There were no significant changes in handgrip strength and endurance, limb volume, or angular velocity after PT. Maximal muscle length was significantly increased. Muscle strength significantly increased for the hamstrings (9% and 19%) and quadriceps (8% and 24%) for the men and women, respectively. Endurance improved for the quadriceps (26% and 39%) and hamstrings (18% and 28%) for men and women, respectively. Functionally, there were significant improvements in the ability to climb stairs, rise from a chair, and walk. Walking time (50 ft) and the difficulty and pain of performing various activities decreased. Most improvements had occurred after 1 month of PT. For the first time, the effects of a PT program have been quantitatively measured for patients with knee OA.

Activities of Daily Living↗

PubMed1993

Effects of a quantitative progressive rehabilitation program applied unilaterally to the osteoarthritic knee.

Decreases in muscular strength, endurance, and angular velocity have previously been demonstrated in the elderly. Osteoarthritis (OA), especially of the knee, may cause further reductions in these parameters and lead to functional limitations. This study measured the effects of a quantitative progressive exercise muscle rehabilitation program (QPE) that was added to a physical therapy (PT) program. Forty subjects (20 men and 20 women) with OA of the knees were randomly selected from a group of volunteers (N = 437) for the 3-month program. Measurements of strength, endurance, angular velocity, and the Jette Functional Status Index were determined before and after 1, 2, and 3 months of the program. The QPE program was composed of isometric, isotonic, isotonic with resistance, endurance, and speed contractions prescribed in a progressive sequence. Muscle strength (14% and 29%) and endurance (38% and 43%) increased significantly (p < 0.05, ANOVA for repeated measures) for both the quadriceps and hamstrings, respectively, after rehabilitation. There were marked decreases in walking time and the difficulty and pain experienced during functional activities.

Activities of Daily Living↗

PubMed1993

Physical condition, activity pattern, and environment as factors in falls by adult care facility residents.

This study surveyed 294 fall incident reports made over a three-year period concerning 95 residents in an adult care facility. We determined the frequencies of fall location, time of day or night, and assessed the precipitating factors from fall descriptions made by residents and/or their care givers. We found that 57% of the falls occurred in the residents' rooms, with private or shared bathrooms as the next most frequent locus. Precipitating factors were surveyed; 50.3% of the fall descriptions implicated environmental features (pieces of furniture were most frequently mentioned), the physical condition of the resident contributed to 24.3% of the falls, and specific physical activities were implicated in 7.9% of the falls. Multiple factors accounted for 6.5% of the total falls. In 17% of the cases, no clear indication of cause was found. Unsafe environments have been implicated as a fall risk factor. Despite adaptations to lessen environmental hazards, a large number of reportable falls occurred in this facility, which was for elderly individuals who were in relatively good health commensurate with their age.

Accidental Falls↗

PubMed1993

Cardiovascular, neuromuscular, and metabolic alterations with age leading to frailty.

As members of our society live longer, a greater percentage of the population will be older. These demographic changes will stress our social and medical delivery system, unless interventions can alter the course leading to frailty. Maximal aerobic power decreases with age, due to a decrease in cardiac output, and is exacerbated by cardiovascular disease. Asymptomatic aging does not reduce cardiovascular function to an extent that would lead to loss of function. Metabolism, endurance, and contraction velocity and muscle strength remain relatively high until 40, 50, and 60 years of age, respectively. After age 60, there are dramatic decreases (approximately 10% per year) which lead to loss of function and independence. The loss of muscle function leads to an increase in the likelihood of falls (approximately 4-fold). Exercise programs utilizing "aerobic" exercise activities do not lead to an increase in muscle function, whereas programs designed specifically for muscle can increase function and, presumably, reduce the risk of falls and injuries.

Adult↗