Flow limitation while breathing HeO2.

Flow limitation during a maximum expiratory flow-volume curve (MEFVC) while breathing air occurs at lung volumes below 70% vital capacity (VC). To evaluate small airways function, use has been made of the volume of isoflow (VisoV), comparing an MEFVC done in air to one done in 80% helium, 20% O2 (HeO2). The VisoV has high intra-subject variability. This study investigated whether this variability was due to an inability to flow limit while breathing HeO2. This would occur if the velocity of expiratory muscle contraction did not result in sufficient intrathoracic pressures to cause dynamic airway compression in the face of increased expiratory flows while breathing HeO2. Seven healthy adult male subjects performed repeated VC expirations of varying effort with an esophageal balloon in place in a body plethysmograph while breathing air and HeO2. The flow-volume curves were matched at residual volume and transpulmonary pressure-flow plots were constructed at volume isopleths of 70, 50, and 25% VC. In air, flow limitation was demonstrated in 3, 6, and 7 subjects at 70, 50, and 25% VC, respectively. In HeO2, flow limitation was achieved in 1 and 4 subjects at 70 and 50% VC. Although one subject demonstrated intermittent glottic closure, the remaining 6 demonstrated flow limitation at 25% VC. We concluded that dynamic airways compression occurs even with the increased flows in HeO2.

Pulse oximetry in sickle cell disease.

Patients with sickle cell disease usually have mild hypoxaemia and their oxyhaemoglobin dissociation curve is shifted to the right. It follows that oxygen saturation in sickle cell disease should be lower than normal. Most subjects in this clinic had normal oxygen saturation by pulse oximetry, however. To improve the understanding of this paradox, arterialised capillary oxygen tension (PO2) and oxygen saturation were compared with simultaneously measured pulse oximeter saturation in 20 children with sickle cell disease. In addition, the PO2 at 50% haemoglobin saturation (P50) was compared with saturation measured by pulse oximetry in all 20 patients. It was found that saturation measured by pulse oximetry was, on the whole, similar to that calculated from the sampled blood. Individual deviations were not random, however, and were partly explained by differences in P50 values. It is concluded that pulse oximetry gives variable results in patients with sickle cell disease and should be used with caution to predict arterial saturation in this patient group.

Pulmonary function abnormalities in childhood sickle cell disease.

Pulmonary function tests in adults with sickle cell disease have shown a restrictive pattern that has been attributed to the sequelae of acute chest syndrome (ACS). We compared pulmonary function test results in 37 children with sickle cell anemia (20 with SS hemoglobin (HbSS), 14 with SC hemoglobin, and 3 with S beta hemoglobin) with those in 22 control subjects matched for sex, race, and height and compared pulmonary function in patients with and without a history of ACS. Of the 10 patients with a history of ACS, all but one had HbSS. Pulmonary function tests measured forced vital capacity (FVC), the diffusion capacity of carbon monoxide, and the plethysmographic determination of lung volumes. The FVC and forced expiratory volume in 1 second (FEV1), expressed as the percentage of the predicted value, were significantly less for those with HbSS with or without a history of ACS than for control subjects (p < 0.05), but the FEV1/FVC ratio, an index of airway obstruction, was normal in all groups. Total lung capacity was also significantly lower in patients with HbSS with or without a history of ACS than in control subjects (p < 0.05), but the ratio of residual volume to total lung capacity, another index of airway obstruction, was normal. We conclude that children with sickle cell disease, particularly those with HbSS, may have abnormally small lungs that function normally relative to their size; clustering of ACS episodes is not specifically associated with the observed abnormality.

Cardiopulmonary response to exercise in anorexia nervosa.

Malnutrition is associated with a number of systemic diseases that are often accompanied by severe exercise limitation. Anorexia nervosa (AN) is a disease characterized by malnutrition due to psychological factors rather than systemic disease. Diminished exercise capacity in AN has been attributed to a loss of muscle mass, dysfunction of remaining muscle, and impaired cardiovascular responses. In order to evaluate the role of malnutrition in the cardiopulmonary response to exercise, nine adolescent girls with AN were evaluated during progressive and steady-state exercise testing using a cycle ergometer. Nutritional status was assessed by body mass percentile (BMP) and percent ideal weight (PIWT). Cardiac output was measured by the indirect (CO2 rebreathing) Fick method. Maximum work capacity (Wmax) was expressed as a percent of predicted for sex and height, and cardiac output as a percent of predicted for oxygen consumption. To ensure that the laboratory values were comparable to the predicted values, a control group consisting of ten adolescents was studied concurrently. Wmax was below the 95% confidence interval in six of nine of the AN group (mean +/- SD: 70 +/- 22% predicted), whereas two of ten controls were below and one above this interval (112 +/- 37%). Wmax correlated with nutritional status (BMP: r = 0.75; P less than 0.001; PIWT: r = 0.8, P less than 0.001). Ventilatory responses for CO2 production at steady state and for Wmax were appropriate in both groups. Cardiac output was appropriate in both the controls (103 +/- 12%) and the AN group (104 +/- 14%).(ABSTRACT TRUNCATED AT 250 WORDS)

Ventilation and gas exchange during exercise in sickle cell anemia.

Adults with sickle cell anemia (SCA) have restrictive lung impairment, increased alveolar dead space, and hypoxemia. These factors, together with increased anaerobic metabolism, are thought to cause exercise hyperventilation. To assess the role of each of these in children, 34 patients with SCA and 16 control subjects performed pulmonary function and exercise tests. Twenty-eight patients with SCA had spirometric values and lung volumes, and all but two patients with SCA had arterial saturation greater than 91% during exercise. Despite a low VO2max (30.07 +/- 6.55 ml/min/kg), the ventilatory anaerobic threshold (VAT) in the patients occurred at a similar %VO2max as in the control subjects (69 +/- 9% versus 63 +/- 12%). The slope of the delta VE/delta VCO2 relationship for sub-VAT work was steeper in the patients (29.4 +/- 6.5 versus 24.7 +/- 5.2, p = 0.01), and the ventilatory equivalent for CO2 (VE/VCO2) in steady-state exercise was greater in the patients than in the control subjects (33.2 +/- 3.5 versus 30.8 +/- 3.5, p = 0.03). End-tidal PCO2 did not differ (38.3 +/- 3.0 versus 39.2 +/- 3.1), indicating equivalent alveolar ventilation. The patients had a higher dead space:tidal volume ratio (VD/VT) than did the control subjects (0.204 +/- 0.033 versus 0.173 +/- 0.024, p = 0.0005). The PaCO2 was significantly lower in those with lower Hb, but there was no difference in pH. In conclusion, children with SCA have an increased exercise ventilatory response caused in part by increased physiologic dead space, and in part by their low Hb. The greater dead space may be the result of sickle cells impairing capillary perfusion to ventilated alveoli.

Cardiac output and oxygen delivery during exercise in sickle cell anemia.

Desaturation in patients with sickle cell anemia (SCA) can lead to intravascular sickling and vascular occlusion. The increased metabolic demands of exercise tend to increase oxygen extraction, giving rise to a fall in saturation in the capillary bed that may predispose to sickling. This could be minimized with an increase in cardiac output. The aims of this study were to assess the role of increased stroke volume (SV) in augmenting cardiac output (Q) and to estimate the role of enlarged arteriovenous O2 content difference in maintaining O2 transport in children with SCA. A group of 30 children with SCA (Hb 65 to 133 g/L) and 16 healthy controls of the same racial group and of similar height and weight performed incremental and steady-state exercise at 50% Wmax. Cardiac output (Q) was measured by the indirect (CO2) Fick method during steady state. The slope of delta HR/delta VO2 during incremental exercise was higher in SCA subjects compared with controls (4.01 +/- 1.73 versus 2.80 +/- 0.61 bpm per ml/min/kg VO2, p = 0.001). Q for VO2 was abnormally high in patients, particularly older ones with lower Hb levels. HR (% predicted) was higher in patients than in controls (106 +/- 11 versus 92 +/- 8% predicted, p less than 0.0001), as was SV (113 +/- 16 versus 98 +/- 14% predicted, p = 0.002). Multiple linear regression of Q % predicted and SV % predicted on Hb and age showed a positive correlation with age and a negative correlation with Hb (r = 0.84 for Q and r = 0.76 for SV).(ABSTRACT TRUNCATED AT 250 WORDS)