Biomedical subjects

R Hughson

Publications and source records attributed to R Hughson.

7 recordsLinked to original sources

PubMed2000

Increases in submaximal cycling efficiency mediated by altitude acclimatization.

To investigate the hypothesis that respiratory gas exchange and, in particular, the O(2) consumption (VO(2)) response to exercise is altered after a 21-day expedition to 6,194 m, five male climbers (age 28.2 +/- 2 yr; weight 76.9 +/- 4.3 kg; means +/- SE) performed a progressive and prolonged two-step cycle test both before and 3-4 days after return to sea level. During both exercise tests, a depression (P < 0.05) in VO(2) (l/min) and an increase (P < 0.05) in minute ventilation (VE BTPS; l/min) and respiratory exchange ratio were observed after the expedition. These changes occurred in the absence of changes in CO(2) production (l/min). During steady-state submaximal exercise, net efficiency, calculated from the rates of the mechanical power output to the energy expended (VO(2)) above that measured at rest, increased (P < 0.05) from 25.9 +/- 1.6 to 31. 3 +/- 1.3% at the lighter power output and from 24.4 +/- 1.3 to 29.5 +/- 1.5% at the heavy power output. These changes were accompanied by a 4.5% reduction (P < 0.05) in peak VO(2) (3.99 +/- 0.17 vs. 3.81 +/- 0.18 l/min). After the expedition, an increase (P < 0.05) in hemoglobin concentration (15.0 +/- 0.49 vs. 15.8 +/- 0.41 g/100 ml) was found. It is concluded that, because resting VO(2) was unchanged, net efficiency is enhanced during submaximal exercise after a mountaineering expedition when the exercise is performed soon after return to sea level conditions.

Acclimatization↗

PubMed1999

Cardiac baroreflex during the postoperative period in patients with hypertension: effect of clonidine.

BACKGROUND: Patients with essential hypertension show altered baroreflex control of heart rate, and during the perioperative period they demonstrate increased circulatory instability. Clonidine has been shown to reduce perioperative circulatory instability. This study documents changes in measures of heart rate control after surgery in patients with essential hypertension and determines the effects of clonidine on postoperative heart rate control in these patients. METHODS: Using a randomized double-blind placebo-controlled design, 20 patients with essential hypertension (systolic pressure >160 mm Hg or diastolic pressure >95 mm Hg for > or =1 yr) were assigned to receive clonidine (or placebo), 6 microg/kg orally 120 min before anesthesia and 3 microg/kg intravenously over 60 min before the end of surgery. The spontaneous baroreflex ("sequence") technique and analysis of heart rate variability were used to quantify control of heart rate at baseline, before induction of anesthesia, and 1 and 3 h postoperatively. RESULTS: Baroreflex slope and heart rate variability were reduced postoperatively in patients given placebo but not those given clonidine. Clonidine resulted in greater postoperative baroreflex slope and power at all frequency ranges compared with placebo (4.9+/-2.9 vs. 2.2+/-2.1 ms/mm Hg for baroreflex slope, 354+/-685 vs. 30+/-37 ms2/Hz for high frequency variability). Clonidine also resulted in lower concentrations of catecholamine, decreased mean heart rate and blood pressure, and decreased perioperative tachycardia and hypertension. CONCLUSIONS: Patients with hypertension exhibit reduced heart rate control during the recovery period after elective surgery. Clonidine prevents this reduction in heart rate control. This may represent a basis for the improved circulatory stability seen with perioperative administration of clonidine.

Analgesics↗

PubMed1997

Sympathovagal effects of spinal anesthesia assessed by the spontaneous cardiac baroreflex.

BACKGROUND: The changes in sympathovagal balance induced by spinal anesthesia remain controversial. The spontaneous baroreflex method allows the continuous assessment of the spontaneous engagement of the cardiac baroreflex, giving an index of sympathovagal balance. The purpose of this study was to follow the effects of spinal anesthesia on spontaneous baroreflex sensitivity. METHODS: Continuous electrocardiogram and noninvasive blood pressure were recorded in 24 patients scheduled for elective inguinal hernia repair and randomly assigned to three groups: (1) no volume loading, (2) volume loading of 15 ml/kg lactated Ringer's solution, and (3) continuous infusion of etilefrine (an ephedrine-like drug). Each patient was studied before, during, and after bupivacaine-induced spinal anesthesia (mean sensory block: T4). Spontaneous baroreflex sensitivity and parameters of time-domain analysis of heart rate variability were calculated from 30 min of recording of each period. RESULTS: No significant change in spontaneous baroreflex slope or parameters of time-domain analysis were observed after regional anesthesia in any group. However, three patients experienced episodes of bradycardia and hypotension in the absence of a high block; these three patients showed an increase in spontaneous baroreflex sensitivity and time-domain parameters. CONCLUSIONS: Using a noninvasive, continuous technique to estimate cardiac sympathovagal balance, no significant variation in autonomic balance induced by spinal anesthesia was observed. However, untoward episodes of bradycardia and hypotension occurred in three patients, who could not be prospectively identified by the parameters studied.

Adjuvants, Anesthesia↗

PubMed1995

Spontaneous cardiac baroreflex in humans. Comparison with drug-induced responses.

We compared two methods of assessment of baroreflex sensitivity in eight supine healthy volunteers during repeated baseline measurements and various conditions of cardiac autonomic blockade. The spontaneous baroreflex method involved computer scanning of recordings of continuous finger arterial pressure and electrocardiogram to locate sequences of three or more beats in which pressure spontaneously increased or decreased, with parallel changes in pulse intervals. The mean regression slope of all these sequences during each study condition was considered to represent the mean spontaneous baroreflex slope. In the drug-induced method, sigmoidal curves were constructed from data obtained by bolus injections of phenylephrine and nitroprusside; the tangents taken at the resting pressure of each of these curves were compared with the mean spontaneous baroreflex slopes. The two methods yielded slopes that were highly correlated (r = .96, P < .001), with significant but similar intraindividual baseline variability. Atropine virtually eliminated the baroreflex slope; subsequent addition of propranolol did not alter it further. Propranolol or clonidine alone increased average baroreflex slope to the extent that they increased resting pulse interval (r = .69 to .83). The spontaneous baroreflex method provides a reliable, noninvasive assessment of human vagal cardiac baroreflex sensitivity within its physiological operating range.

Adult↗

PubMed1986

Internal work and physiological responses during concentric and eccentric cycle ergometry.

Internal mechanical work during cycling, required to raise and lower the legs and change their velocities, is shown to be an important factor when interpreting physiological responses to cycle ergometer exercise. The internal work required to move the legs during concentric and eccentric cycle ergometry at different speeds and workloads was calculated from segmental energy changes determined using cinematography and directly using an eccentric ergometer. The mean internal work rates obtained at pedal frequencies of 30, 60 and 90 min-1 were 11.5, 20 and 62 W respectively. When these estimates were added to the external work rates, they increased concentric and decreased eccentric work rates. The largest differences were seen at low work rates and high pedal frequencies during which concentric work rates increased by 51% and eccentric decreased 60% by the inclusion of internal work. When comparisons of concentric and eccentric cycling at equal uncorrected work rates were made, neglecting to include internal work introduced errors ranging from 12 to 97%. The calculated estimates of internal work agreed well with the power supplied by the eccentric ergometer to move the legs passively. The investigations show that the inclusion of internal work is important when comparing physiological responses during concentric and eccentric ergometry, especially when pedal frequencies exceed 60 min-1 and when work rates are small.

Adult↗

PubMed1986

Children in competitive sports--a multi-disciplinary approach.

This article is divided into two parts: Part 1 consists of the position stand of The Canadian Association of Applied Sport Sciences on the involvement of children in competitive sports, and Part II presents scientific background and rationale pertinent to the position statements. Each part is divided into major categories reflecting the multi-disciplinary concerns of the participation of pre- and post-pubescent children in sport situations at all levels. Psychological considerations focus on the child learning a sense of competence and control through sport participation. Success in a sport should not be based solely on winning, but on one's own performance and attained goals. Sport involvement can provide one important avenue for a child's social development. Non-aggressive behaviour and a constructive problem-solving approach should be encouraged. Any form of discrimination towards sport participation or competition should be discouraged. From the physiological and medical point of view, it should be recognized that each child is different in his/her response and tolerance to exercise due to a great range of variability in growth rates, anthropometric indices, gender and state of health, even in children of a similar chronological age. Younger prepubertal children should be encouraged to participate in a wide variety of motor skills, whereas older post-pubertal children can become more specialized in their training and sport participation. A child's performance and adaptation to training should not be directly compared to an adult's as significant differences exist, especially during the years of accelerated growth. Environmental exercise tolerance is also more limited to children than adults. In younger children repetitive heavy loading of the musculoskeletal system should be approached with caution. With proper equipment design and usage, and rule modifications, serious injuries can be avoided. Medical disabilities should be evaluated on an individual basis and should not necessarily preclude a child's participation. Teachers, parents and coaches should have a thorough understanding of the implications of children involved in sports and adhere to the recommendations reviewed in this statement.

Athletic Injuries↗

PubMed1979

The energy cost of cross-country skiing among elite competitors.

The energy costs of skiing with the diagonal stride technique was investigated in 15 members of the men's and women's national cross-country ski teams and in 5 recreational skiers. Oxygen uptake was measured directly by means of a portable bag-method for each subject during level skiing at 3 different skiing speeds. The oxygen cost of double poling vs. diagonal stride techniques was also measured in 3 subjects during level skiing. Although a strong linear relationship was found between VO2 and speed of skiing (r = 0.868, p less than 0.001), there was considerable variation even among elite competitors. The VO2-skiing speed relationship was parallel to that obtained for running, but the O2 cost of skiing was found to be 10--12 ml/kg in excess of that predicted for level running at the same speed. On flat terrain, the O2 cost of the double poling technique as used in fast skiing was found to be higher than that for diagonal striding.

Female↗