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H T Robertson

Publications and source records attributed to H T Robertson.

At least 55 records · Page 3Linked to original sources
PubMed1983

Ventilation-perfusion relationships after hemorrhage and resuscitation: an inert gas analysis.

Previous investigations suggest that ventilation-perfusion (VA/Q) relationships after hemorrhagic shock are primarily dependent on regional distribution of pulmonary blood flow and implicated early VA/Q heterogeneity secondary to disproportionate redistribution of pulmonary blood flow to dependent lung regions. Multiple inert gas elimination analysis, as described by Wagner et al. (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 36: 588-599, 1974), was applied to a standard hemorrhagic shock preparation to test this hypothesis. Soon after hemorrhage, VA/Q distributions shifted homogeneously into high VA/Q compartments, preserving base-line VA/Q relationships around a new mean VA/Q ratio. Although the mean VA/Q and VA/Q distribution returned to base line after resuscitation with autologous blood, absolute dead space ventilation persisted. Gas exchange defects included increased Bohr dead space ventilation, which could be attributed to 1) a homogeneous shift of VA/Q distributions into high VA/Q compartments, and 2) new absolute dead space ventilation associated with observed intravascular leukostasis and vascular occlusion. In contrast to previous investigations, these data suggest that VA/Q heterogeneity does not occur after hemorrhage, but rather pulmonary blood flow decreases proportionately throughout all lung regions, preserving base-line VA/Q patterns around a new mean VA/Q ratio.

Animals↗
PubMed1983

Mechanisms of physiological dead space response to PEEP after acute oleic acid lung injury.

In acute increased-permeability edema, the Bohr physiological dead space (VD/VTCO2) can be influenced by changes in anatomic dead space, ventilation-perfusion (VA/Q) heterogeneity, shunt, and the Haldane effect. We used the multiple inert gas elimination technique to assess the effect of positive end-expiratory pressure (PEEP) on each of these components of VD/VTCO2 in 14 pentobarbital-anesthetized dogs with increased permeability edema induced by infused oleic acid. PEEP of 5, 10, 15, and 20 cmH2O was applied in random sequence. Following injury VD/VTCO2 increased. It decreased with 5 or 10 cmH2O PEEP but increased progressively at higher PEEP levels. The decrease in VD/VTCO2 at 5 or 10 cmH2O PEEP was due to reductions in shunt and midrange VA/Q heterogeneity. The increase in VD/VTCO2 that occurred with higher PEEP levels was due to increased ventilation to high VA/Q regions and a larger anatomic dead space. Haldane effect magnified the shunt component of VD/VTCO2 but reduced the influence of midrange VA/Q heterogeneity.

Acute Disease↗
PubMed1983

Iron repletion decreases maximal exercise lactate concentrations in female athletes with minimal iron-deficiency anemia.

We studied the effect of 2 weeks of iron therapy on exercise performance and exercise-induced lactate production in trained women athletes: six control subjects with normal parameters of iron status and nine with mild iron-deficiency anemia defined by low Fe/TIBC, ferritin, and minimally decreased Hgb values. Iron therapy improved the abnormal measures of iron status and low Hgb in the second group to normal. Exercise performance in a progressive work-exercise protocol on a bicycle ergometer to exhaustion was unchanged after iron therapy in both groups; however, blood lactate levels at maximum exercise in the iron-deficient group decreased significantly from 10.3 +/- 0.6 mmol/L before therapy to 8.42 +/- 0.7 after therapy (p less than 0.03). The control subjects did not significantly alter lactate levels after maximal exercise on iron compared to placebo: 8.3 +/- 0.8 mmol/L vs. 8.5 +/- 0.7. Although there was not a significant difference in maximum exercise performance after iron therapy, these data support animal experiments implying that iron may play a role in oxidative metabolism and that minimal decreases in Hgb may impair arterial oxygen content enough to affect aerobic metabolism. In addition, these findings may have important implications for competitive women athletes in whom mild iron deficiency may go unnoticed.

Acidosis↗
PubMed1982

Augmentation of exercise ventilation by medroxyprogesterone acetate.

The influence of medroxyprogesterone acetate (MPA) on exercise performance was studied in a double-blind cross-over trial using six normal males to compare the exercise performance changes to those observed in a previous study of exercise responses of female subjects during the follicular and luteal phase of the menstrual cycle. A maximal progressive work exercise test on a cycle ergometer was performed after 2 weeks of placebo or MPA administration. Although five of six subjects spontaneously complained of increased exertional dyspnoea on MPA, no significant decreases were documented in maximal exercise time or in maximal oxygen consumption. A mean increase in exercise ventilation of 19% at low levels of exertion and 26% at high levels of exertion was documented, but no subject demonstrated evidence of ventilatory limitation. The increases in exercise ventilation observed in these male subjects after MPA administration were larger than those observed in the previous study comparing exercise ventilatory responses during follicular and luteal phases of the menstrual cycle. It seems possible that some other exercise-related modulator of the ventilatory response to exercise under the influence of progesterone is present in either male subjects receiving MPA or women with normal hormonal cycles.

Adult↗
PubMed1982

Respiratory and inert gas exchange during high-frequency ventilation.

Pulmonary gas exchange during high-frequency low-tidal volume ventilation (HFV) (10 Hz, 4.8 ml/kg) was compared with conventional ventilation (CV) and an identical inspired fresh gas flow in pentobarbital-anesthetized dogs. Comparing respiratory and infused inert gas exchange (Wagner et al., J. Appl. Physiol. 36: 585--599, 1974) during HFV and CV, the efficiency of oxygenation was not different, but the Bohr physiological dead space ratio was greater on HFV (61.5 +/- 2.2% vs. 50.6 +/- 1.4%). However, the elimination of the most soluble inert gas (acetone) was markedly enhanced by HFV. The increased elimination of the soluble infused inert gases during HFV compared with CV may be related to the extensive intraregional gas mixing that allows the conducting airways to serve as a capacitance for the soluble inert gases. Comparing as exchange during HFV with three different density carrier gases (He, N2, and Ar), the efficiency of elimination of Co2 or the intravenously infused inert gases was greatest with He-O2. However, the alveolar-arterial partial pressure difference for O2 on He-O2 exceeded that on N2-O2 by 5.4 Torr during HFV. The finding agrees with similar observations during CV, suggesting that this aspect of gas exchange is not substantially altered by HFV.

Animals↗
PubMed1982

The effects of expiratory positive airway pressure on the resolution of oleic acid-induced lung injury in dogs.

It is not known whether positive end-expiratory pressure (PEEP) merely improves gas exchange in patients with the adult respiratory distress syndrome or also affects the resolution of their lung injury. We examined the effects of expiratory positive airway pressure (EPAP), a form of PEEP, on 13 pairs of spontaneously breathing mongrel dogs with permanent tracheostomies that were subjected to acute lung injury from oleic acid. One member of each pair was treated with 10 cm H2O EPAP by means of a special valve attached to its tracheostomy tube; the other member breathed through the tracheostomy tube alone. The EPAP was applied 3 h after an intravenous injection of 0.06 ml/kg oleic acid and continued for a total of 21 h. Functional residual capacity (FRC) was increased to preinjury values in the EPAP-treated dogs at 3, 12, and 24 h compared with that in the untreated dogs. The PaO2 was higher and the venous admixture (Qva/QT) was lower in the EPAP-treated dogs compared with that in the untreated dogs at 3 and at 12 h. However, over the 7 days after removal of EPAP no significant differences were noted between the 2 groups in FRC, PaO2, Qva/QT, inert gas elimination profiles, mortality, final lung compliance to initial lung compliance differences, lung water to dry lung weight ratios, or histologic features. We conclude that EPAP improves gas exchange during its administration but has no demonstrable effect on the resolution of lung injury induced by oleic acid in dogs.

Animals↗
PubMed1981

Increasing intracranial pressure with air causes air embolism, not neurogenic pulmonary edema.

In an effort to duplicate a previous model of neurogenic pulmonary edema (NPE), we maintained intracranial pressure (PIC) at 20 Torr below mean arterial pressure in six closed-chested dogs anesthetized with alpha-chloralose and urethan. This was accomplished by infusing 1) isotonic saline (NS), 2) a gas mixture of 80% helium and 20% oxygen (HeO2), or 3) 100% carbon dioxide (CO2) through a trephined hole into the subdural space. Three more animals were studied with the same protocol after thoracotomy to permit Doppler examination for bubbles in the left pulmonary artery. Significant increases in pulmonary artery pressure, pulmonary vascular resistance, physiological shunt, dead space fraction, and hypoxemia were recorded when Pic was elevated by HeO2 infusion but not during infusion of NS or CO2. Pulmonary gas-bubble embolism was suggested by an increase in the fraction of helium in expired gas during HeO2 infusion and confirmed by Doppler recordings. We conclude that increasing Pic with air produces the physiological changes of air embolism; this is not a satisfactory model for investigating NPE.

Animals↗
PubMed1981

Respiratory drives and exercise in menstrual cycles of athletic and nonathletic women.

To investigate the influence of the midluteal and midfollicular phases of the menstrual cycle on exercise performance and ventilatory drives, we studied six outstanding female athletes, six controls with normal menstrual cycles, and six outstanding athletes who were amenorrheic. In all menstruating subjects resting minute ventilation (Ve) and mouth occlusion pressures (P0.1) were higher in the luteal phase (p less than k0.0001 and p less than 0.02, respectively),. Hypoxic (expressed as the hyperbolic shape parameter A) and hypercapnic (expressed as S, deltaVE/delta PAco2) ventilatory responses were increase in the luteal phase (p less than 0.01). The athletes had lower A values during the luteal phase than the nonathletes (p less than 0.001). Maximal exercise response, expressed either as total exercise time or maximum O2 consumption or CO2 production (VO2 max or Vco2 max) was decreased during the luteal phase but was significantly different at a p less than 0.05 level only among the nonathletes. Ventilatory equivalent (VE/VO2) during progressive exercise on a bicycle ergometer was significantly increased during the luteal phase. The amenorrheic athletes showed no changes between the two test periods. The luteal phase of the menstrual cycle induced increases in ventilatory drives and exercise ventilation in both athletes and controls, but the athletes, in contrast to controls, demonstrated no significant decrease in exercise performance in the luteal phase.

Adolescent↗
PubMed1981

Ventilation and perfusion alterations after smoke inhalation injury.

Previous studies of human victims of smoke inhalation injury have demonstrated retention of intravenously infused 133xenon2, 6 suggesting either: (1) true intrapulmonary shunting (Qs) secondary to alveolar collapse, flooding, or obliteration, or (2) perfusion of low ventilation/perfusion compartments (low VA/Q) secondary to bronchospasm, bronchial constriction, or partial bronchial occlusion by cellular debris. To differentiate between and quantitate the relative contribution of intrapulmonary shunt versus low VA/Q compartments, multiple inert gas analysis, as described by Wagner et al.,12 was applied to human victims of smoke inhalation. Studies of an animal model of injury were subsequently performed to confirm these observations. These experiments suggest that early alterations of ventilation and perfusion resulted from increased high VA/Q and dead-space ventilation. Late alterations included significantly increased perfusion of low VA/Q compartments and return of high VA/Q ventilation to baseline levels. True intrapulmonary shunting was notably absent. This physiologic sequence may represent early regional pulmonary vasospasm followed by regional bronchial obstruction and gradual alveolar secondary to bronchospasm, bronchial edema, or partial occlusion by cellular debris.

Airway Obstruction↗
PubMed1979

Gas exchange abnormalities produced by venous gas emboli.

Bubbles of either He, N2 or SF6 were infused intravenously into anesthetized dogs at a rate of 0.2 ml/kg/min. Alterations in pulmonary gas exchange were quantitated by the invert gas elimination method during control, steady state infusion and resolution phases. The hypoxemia produced was predominantly due to regions of low VA/Q rather than pure shunt, and the increase in physiological dead space was due to the addition of high VA/Q regions rather than 'pure' dead space. The VA/Q distribution returned to normal within 30 minutes of stopping the He or N2 bubbles, but remained abnormal for longer periods with SF6 bubbles. The net elimination of insoluble gases (such as He or N2) was only slightly impaired by bubble emboli, provided the cardiac output remained constant. Early pulmonary edema from bubble embolization was documented by increased wet weight/dry weight ratio, but the increased lung water was not apparent on histological examination. This form of pulmonary embolus is unique in that there is a constant fraction of the vasculature blocked although any given region with embolus is undergoing continuous resportion of the bubble. This produced a partial obstruction of the affected gas exchange units which manifests as regions of high VA/Q rather than pure dead space.

Animals↗
PubMed1978

Lung injury following a 50-metre fall into water.

The pulmonary complications of a 50-metre fall to the water (a form of suicide attempt producing 87% mortality) were studied in 15 survivors. Presenting findings included crackles, haemoptysis, and hypotension. The alveolar-arterial oxygen difference was greater than 150 mmHg (20 kPa) in nine subjects on admission. Ventilatory failure developed in 10 of the patients, including all of those with massive haemoptysis. Radiographic findings included pneumothorax and diffuse pulmonary opacities adjacent to the area of impact. Pneumothorax developed within 12 hours of admission in 10 of 15 subjects but was associated with rib fractures in only four subjects. The clinical course of the condition is consistent with the hypothesis that the traumatic pulmonary tears produced interstitial emphysema, with subsequent development of pneumomediastinum, subcutaneous emphysema, and pneumothorax. Pneumothorax is a common complication of severe lung contusion even in the absence of penetrating pleural injury.

Adult↗
PubMed1977

Disorganized medicine.

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American Medical Association↗