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Biomedical subjects

D Robertshaw

Publications and source records attributed to D Robertshaw.

At least 19 recordsLinked to original sources
PubMed1999

Effect of locomotor respiratory coupling on respiratory evaporative heat loss in the sheep.

During galloping, many animals display 1:1 coupling of breaths and strides. Locomotor respiratory coupling (LRC) may limit respiratory evaporative heat loss (REHL) by constraining respiratory frequency (f). Five sheep were exercised twice each, according to a five-step protocol: 5 min at the walk, 5 min at the trot (trot1), 10 min at the gallop, 5 min at the trot (trot2), and 5 min at the walk. Rectal temperature (T(re)), stride frequency, f, REHL, and arterial CO(2) tension and pH were measured at each step. Tidal volume (VT) was calculated. LRC was observed only during galloping. The coupling ratio remained at 1:1 while VT increased continuously during galloping, causing REHL to increase from 2.9 +/- 0.2 (SE) W/kg at the end of trot1 to a peak of 5.3 +/- 0.3 W/kg. T(re) rose from 39.0 +/- 0.1 degrees C preexercise to 40.2 +/- 0.2 degrees C at the end of galloping. At the gallop-trot2 transition, VT fell and f rose, despite a continued rise in T(re). Arterial CO(2) tension fell from 36.5 +/- 1.1 Torr preexercise to 31.8 +/- 1.4 Torr by the end of trot1 and then further to 21.5 +/- 1.2 Torr by the end of galloping, resulting in alkalosis. In conclusion, LRC did not prevent increases in REHL in sheep because VT increased. The increased VT caused hypocapnia and presumably elevated the cost of breathing.

Animals↗
PubMed1998

Thermal drive contributes to hyperventilation during exercise in sheep.

The etiology of exercise hypocapnia is unknown. The contributions of exercise intensity (ExInt), lactic acid, environmental temperature, rectal temperature (Tre), and physical conditioning to the variance in arterial CO2 tension (PaCO2) in the exercising sheep were quantified. We hypothesized that thermal drive contributes to hyperventilation. Four unshorn sheep were exercised at approximately 30, 50, and 70% of maximal O2 consumption for 30 min, or until exhaustion, both before and after 5 wk of physical conditioning. In addition, two of the sheep were shorn and exercised at each intensity in a cold (<15 degrees C) environment. Tre and O2 consumption were measured continuously. Lactic acid and PaCO2 were measured at 5- to 10-min intervals. Data were analyzed by multiple regression on PaCO2. During exercise, Tre rose and PaCO2 fell, except at the lowest ExInt in the cold environment. Tre explained 77% of the variance in PaCO2, and ExInt explained 5%. All other variables were insignificant. We conclude that, in sheep, thermal drive contributes to hyperventilation during exercise.

Animals↗
PubMed1995

Metabolic adaptations for desert survival in the Bedouin goat.

Energy conservation is a key adaptation for desert survival in the Bedouin goat. When food is scarce, metabolism is reduced and body weight can be maintained indefinitely on less than one-half of normal intake. We hypothesized that metabolism would be turned down during both rest and exercise, but it was not. It was low when animals rested and returned to normal during exercise. We expected catecholamines and thyroid hormones would modulate metabolism, but they did not. The reduction in metabolism preceded any change in thyroid hormone concentrations, and infusions of epinephrine did not restore reduced metabolism to normal levels. Finally, we expected the gut would be the major organ system involved in the metabolic reduction because less food is eaten, processed, and absorbed. Contrary to our expectations, we found that muscle is the primary organ system responsible for the reduction. It appears that the adaptations of the Bedouin goat for surviving on limited food supplies involve different organ systems and different modulators to reduce metabolism from those known for other mammals.

Adaptation, Physiological↗
PubMed1992

Determination of maximal oxygen consumption in exercising pregnant sheep.

Previous work with pregnant ewes has shown that acute bouts of exercise may cause changes in plasma hormone concentrations, blood flow distribution, and maternal and fetal temperatures. However, most of these studies do not quantify the chosen exercise intensity through measurement of oxygen consumption (VO2). Therefore the purpose of this study was to statistically model the VO2 response of pregnant sheep to treadmill (TM) exercise to determine the exercise intensities (% maximal VO2) of previous studies. Ewes with either single (n = 9) or twin (n = 5) fetuses were studied from 100 to 130 days of gestation. After 1-2 wk of TM habituation, maximal VO2 (VO2max) was determined by measurements of VO2 (open flow-through method) and blood lactate concentration. VO2 was measured as a function of TM incline (0, 3, 5, and 7 degree) and speed (0.8-3.4 m/s). VO2max averaged 57 +/- 7 (SD) ml.min-1.kg-1, and peak lactate concentration during exercise averaged 22 +/- 2 mmol/l. The relationship between VO2 (ml.min-1.kg-1) and incline (INC) and speed (SP) [VO2 = 0.70(INC) + 13.95(SP) + 1.07(INC x SP) - 1.18] was linear (r2 = 0.94). Our findings suggest that most previous research used exercise intensities less than 60% VO2max and indicate the need for further research that examines the effect of exercise during pregnancy at levels greater than 60% VO2max.

Animals↗
PubMed1991

Direct referral hearing aid provision in the over sixties age group.

A prospective study was designed in which General Practitioners were issued with a standard referral letter for hearing aid provision. Unknown to the General Practitioner an independent otolaryngologist assessment was obtained at the time of first attendance. Three hundred consecutive patients selected by General Practitioners applying these guidelines were seen in a designated hearing aid clinic staffed by audiological technicians of senior grade or above. Referral pro formata were incomplete in 75 patients who were not assessed. Ninety-four patients (31 per cent) (95 per cent confidence interval 29-36 per cent) were accepted by the audiologist. Obstructing wax was the most common criterion failed. Clinical agreement between audiologist and otolaryngologist was 57 per cent greater than chance. None of the cases of clinical disagreement altered treatment. A direct referral system as proposed could have processed only 31 per cent of 300 referrals. However, experienced technical staff reliably detected otological pathology and with aural toilet facilities 91 per cent of 225 patients (confidence interval 88-94 per cent) were aided.

Aged↗
PubMed1990

Influence of dehydration and watering on camel red cell size: a scanning electron microscopic study.

Three young female camels were subjected to an eleven day period of dehydration followed by a single large drink. Blood haematocrit and plasma protein concentration were monitored regularly during dehydration and for 48 h following watering. Blood samples were taken at regular intervals, before and after watering, and prepared for scanning electron microscopy (SEM) for analysis of red cell size and shape. Plasma protein concentration did not change rapidly on watering implying that the camel has homeostatic mechanisms which regulate plasma osmolarity by controlling the rate at which large volumes of water are absorbed on drinking. By SEM, camel red cells were elliptical in shape with mean surface dimensions of 6.5 microns x 4.0 microns with an estimated minimum thickness at mid point of 0.95 microns: neither their shape constant nor size changed on dehydration or watering corroborating the absence of major and rapid changes in osmolarity.

Animals↗
PubMed1990

Cold-induced changes in breathing pattern as a strategy to reduce respiratory heat loss.

Thermoregulatory benefits of cold-induced changes in breathing pattern and mechanism(s) by which cold induces hypoventilation were investigated using male Holstein calves (1-3 mo old). Effects of ambient temperatures (Ta) between 4 and 18 degrees C on ventilatory parameters and respiratory heat loss (RHL) were determined in four calves. As Ta decreased, respiratory frequency decreased 29%, tidal volume increased 35%, total ventilation and RHL did not change, and the percentage of metabolic rate attributed to RHL decreased 26%. Total ventilation was stimulated by increasing inspired CO2 in six calves (Ta 4-6 degrees C), and a positive relationship existed between respiratory frequency and expired air temperature. Therefore, cold-exposed calves conserve respiratory heat by decreasing expired air temperature and dead space ventilation. Compared with thermoneutral exposure (16-18 degrees C), hypoventilation was induced by airway cold exposure (4-6 degrees C) alone and by exposing the body but not the airways to cold. Blocking nasal thermoreceptors with topical lidocaine during airway cold exposure prevented the ventilatory response but did not lower hypothalamic temperature. Hypothalamic cooling (Ta 16-18 degrees C) did not produce a ventilatory response. Thus, airway temperature but not hypothalamic temperature appears to control ventilation in cold-exposed calves.

Acclimatization↗
PubMed1990

Effect of bilateral splanchnic nerve section on adrenal function in the ovine fetus.

The effect of bilateral splanchnic nerve (SPLX) section in fetal sheep [116-121 days gestational age (dGA)] on subsequent adrenocortical function was investigated. Fetal cortisol release was stimulated by 1) ACTH-(1-24) administration (100 ng/min for 15 min) at 126-129 and at 132-135 dGA, and 2) nitroprusside-induced hypotension (50% reduction in fetal arterial blood pressure for 10 min) at 129-132 and 136-139 dGA. No differences were observed between SPLX and control fetuses (CONT) in basal arterial plasma concentrations of cortisol from 126-141 dGA. A significant effect of fetal age on basal cortisol was observed in both SPLX and CONT fetuses from 126-141 dGA. A significant (P less than or equal to 0.05) increase in fetal arterial concentrations of cortisol was achieved by ACTH-(1-24) infusion in SPLX and CONT and did not differ between groups at either 126-129 or 132-135 dGA. Hypotension induced a significant increase in fetal plasma cortisol concentrations in SPLX and CONT fetuses (P less than or equal to 0.05). SPLX fetuses secreted significantly less cortisol in response to hypotension than CONT fetuses at both 129-132 and 136-139 dGA (P less than 0.05). Fetal arterial plasma concentrations of immunoreactive ACTH in response to hypotension were not different between CONT and SPLX fetuses. We estimated the half-life of endogenous fetal plasma cortisol after both hypotension and infusion of ACTH-(1-24). There were no differences between either method of inducing cortisol release on the endogenous cortisol half-life, nor were any differences in cortisol half-life observed between SPLX and CONT. At 136-139 dGA the adrenomedullary response to hypotension was abolished in SPLX, confirming completeness of denervation. In conclusion, the splanchnic nerves do not appear to be involved in the normal increase in basal fetal plasma cortisol observed in late gestation in fetal sheep. However, splanchnic nerve modulation of secretion of cortisol in response to stress may be involved in the increased fetal adrenal sensitivity to stress observed late in gestation.

Adrenal Glands↗
PubMed1989

Brain cooling and respiratory heat exchange in camels during rest and exercise.

Respiration in relation to brain temperature (Tb) and body temperature (Tc) were investigated in two camels at rest and one during exercise (running at 10 km/h). The animals were subjected to natural ambient conditions (day: 25-30 degrees C, relative humidity (RH) about 65%; night: 15-20 degrees C, RH approx. 90%). They were studied when fully hydrated and during progressive dehydration by up to 15% of initial weight. At low Tc (less than 38 degrees C) Tb greater than Tc by approximately 0.2 degrees C, at higher Tc significant brain cooling was observed by as much as 1.5 degrees C during exercise. Minute ventilation (VE) and respiratory rate (f) increased with Tc such that tidal volume was constant and similar at rest and during exercise (Tc-Tb) increased linearly with f and hence VE. The cooling, dependent on turbinate heat exchange was related to certain features of the air flow pattern and f which have also been described in other large mammals.

Animals↗
PubMed1989

A system for accelerated provision of hearing aids to residents of homes for the elderly.

A study was undertaken to detect undiagnosed deafness in elderly people, living in Part III Residential Homes in North Tees, South Tees and Hartlepool Health Districts, to provide hearing aids and to estimate the subsequent success in rehabilitation. The residents were referred by the senior staff in the homes and assessed by a doctor and audiology technician in a domiciliary setting. Those found to have a significant hearing impairment were prescribed hearing aids without formal pure tone audiometry. A pilot study compared the method of hearing evaluation employed with such conventional testing. Six months after fitting, the degree of compliance with aiding was assessed. The results show a significant level of undiagnosed deafness in the community and, with this method of provision, an acceptance rate of 41.2 per cent of those recommended for aiding at six months which is higher than suggested by previous similar studies of this population.

Aged↗
PubMed1987

Respiration in heat stressed camels.

Respiration and heat exchange in relation to brain temperature (Th) and body temperature (Tb) were investigated in four heat stressed camels subjected daily to high temperature (47 degrees C) in a climate chamber while resting when hydrated and dehydrated by approximately 10%, 15% and 20% of initial weight. Diurnally Tb followed patterns described previously. Th was usually 0.2-0.5 degrees C greater than Tb: occasional reversals with brain cooling were observed. Minute ventilation increased with Tb: above 37.5 degrees C it was approximately half as much in dehydrated as in hydrated animals. Respiratory frequency increased with Tb up to 60/min. Tidal volume fell with increasing frequency; above 25 breaths/min, tidal volume approximated dead space volume. Exhaled air was almost always unsaturated with no systematic effect of dehydration. Metabolic rate fell on dehydration reducing ventilatory demand. Th and Tb were measured in two of the animals walking outdoors: then Th fell below Tb if exercise exceeded 30 min. The data indicate that heat stressed camels pant, but turbinate vasoconstriction in a hot environment prevents cooling of the brain by carotid rete heat exchange.

Animals↗
PubMed1985

Pulmonary vascular responsiveness in cold-exposed calves.

The pulmonary vascular responses to acute hypoxia and to infusions of histamine and 5-hydroxytryptamine (5-HT) were recorded in unanesthetized standing bull calves under neutral (16-18 degrees C) and cold (3-5 degrees C) temperature conditions. Cold exposure alone resulted in a significant increase in pulmonary arterial wedge pressure from 10.2 +/- 3.5 to 15.9 +/- 4.9 Torr (1 Torr = 133.322 Pa). Resistance to blood flow between the pulmonary wedge and the left atrium significantly increased from 0.50 +/- 0.51 to 1.21 +/- 0.78 mmHg . L-1 . min-1 (1 mmHg = 133.322 Pa) with cold exposure. This apparent pulmonary venoconstrictor response to cold exposure was further evaluated to determine if hypoxia, histamine, or 5-HT responsiveness was altered by cold exposure. Twelve minutes of hypoxia increased pulmonary arterial and systemic arterial pressures, heart rate, and respiratory rate similarly in cold and neutral temperatures. Cold exposure did not alter the dose-related reductions of systemic arterial and pulmonary arterial pressures in response to histamine. Similarly, the decreases in systemic arterial pressure and heart rate and increases in pulmonary arterial and left atrial pressures in response to 5-HT were not significantly different in cold and neutral conditions. It was concluded that acute, mild cold exposure results in an increase in resistance to blood flow in the pulmonary venous circulation without a general increase in pulmonary vascular reactivity, as measured by responses to hypoxia, histamine, and 5-HT.

Animals↗
PubMed1985

Interaction between cold and altitude exposure on pulmonary circulation of cattle.

Hereford calves were exposed in a temperature-controlled hypobaric chamber to environmental temperatures of -2 to 1 degree C (cold) at altitudes of 1,524 m (resident altitude) and 3,048 m 1) to characterize the effects of cold exposure on the pulmonary circulation; 2) to examine the role of cold-induced hypoventilation on the pulmonary circulation; and 3) to examine the interaction between cold and hypoxia on the pulmonary circulation. Cold exposure produced a significant increase in pulmonary arterial pressure (Ppa), pulmonary arterial wedge pressure (Ppaw), and pulmonary vascular resistance (PVR) at both 1,524 and 3,048 m without affecting cardiac output. Concomitantly, cold exposure caused reductions in minute ventilation, respiratory rate, end-tidal O2 tension (PETO2), and arterial O2 tension (PaO2). Tidal volume, end-tidal CO2 tension, and arterial CO2 tension increased. Neither arterial pH nor O2 consumption changed during cold exposure. These results indicated that both pulmonary arterial and venous vasoconstriction were responsible for the pulmonary hypertension associated with cold exposure. Acute exposure to 3,048 m during cold exposure produced increases in Ppa and PVR that were similar to those elicited by cold exposure at 1,524. It was concluded that altitude exposure neither attenuated nor potentiated the effect of cold exposure on the pulmonary circulation; rather, altitude and cold exposure interacted additively. O2 administered during cold exposure to restore PETO2 and PaO2 to control values partially restored Ppa and PVR to control values. This suggested that a portion of the pulmonary hypertension associated with cold exposure was due to hypoxic pulmonary vasoconstriction elicited by the cold-induced alveolar hypoventilation.

Altitude↗
PubMed1984

Bone mineral content and menstrual regularity in female runners.

The relationship between bone mineral content and menstrual regularity in 10 amenorrheic runners (0-3 menses during the past year), 12 runners with regular menstrual cycles (10-12 menses during the past year), and 15 non-athletic women with regular menstrual cycles was investigated. Comparisons of the two groups of runners indicated no significant differences in body fatness, average weekly running distance, or average daily intake of calcium (Ca), phosphorus (P), and Ca/P ratios. Mean bone mineral content for the three groups, measured by photon absorptiometry, was 0.508, 0.529, and 0.544 g X cm-2, respectively, at 3 cm distal radius, and 0.707, 0.700, and 0.707 g X cm-2, respectively, at one-third distal radius, indicating no significant differences among the groups (P less than 0.05). However, a significant relationship (r = 0.77) was noted between bone mineral content and body fatness only in the amenorrheic runners. Within the amenorrheic population, the five thinnest runners had significantly lower mean bone mineral content values at 3 cm distal radius (0.457 g X cm-2) than the five runners with higher relative body fatness (0.559 g X cm-2). We conclude, therefore, that amenorrhea, independent of body composition, was not related to reduced bone mineral content in female runners. However, the combination of excessive thinness and amenorrhea may, in fact, predispose female athletes to reduced bone mass.

Adipose Tissue↗
PubMed1984

Delayed menarche in swimmers in relation to age at onset of training and athletic performance.

Competitive swimmers have been considered to be different from other female athletes in that their mean age at menarche is similar to that of nonathletes. However, it was hypothesized that if the delayed menarche observed in athletes of other sports is caused by prepubertal training, then swimmers should also exhibit delayed menarche as the majority of swimmers begin training prior to puberty. Furthermore, if early prepubertal training is the important factor in delaying menarche, then it was hypothesized that a relationship between performance and age at menarche in swimming is unlikely to exist. Thus, 345 competitive female swimmers and 549 control subjects completed questionnaires concerning general health, athletic training history, and age at menarche. Results indicated that, as a population, the mean age at menarche of the swimmers (13.4 yr) was significantly later than the controls (13.0 yr). When swimmers and controls were compared on an age-group basis, it was found that the difference in age at menarche was due to the data obtained from the older and more highly competitive swimmers. Assigning swimmers to different competitive levels or by performance in specific swimming events (50- or 100-yd freestyle; 45.7- or 91.4-m, respectively) indicated a significantly later age at menarche for the more competitive swimmers. Thus, there is evidence that the age at menarche and subsequent athletic performance in swimming are related; the later menarche observed in swimmers appears to be associated with factors that select for superior performance.

Adolescent↗