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William A Whitelaw

Publications and source records attributed to William A Whitelaw.

5 recordsLinked to original sources
PubMed2005

RV filling modulates LV function by direct ventricular interaction during mechanical ventilation.

During mechanical ventilation, phasic changes in systemic venous return modulate right ventricular output but may also affect left ventricular function by direct ventricular interaction. In 13 anesthetized, closed-chest, normal dogs, we measured inferior vena cava flow and left and right ventricular dimensions and output during mechanical ventilation, during an inspiratory hold, and (during apnea) vena caval constriction and abdominal compression. During a single ventilation cycle preceded by apnea, positive pressure inspiration decreased caval flow and right ventricular dimension; the transseptal pressure gradient increased, the septum shifted rightward, reflecting an increased left ventricular volume (the anteroposterior diameter did not change); and stroke volume increased. The opposite occurred during expiration. Similarly, the maneuvers that decreased venous return shifted the septum rightward, and left ventricular volume and stroke volume increased. Increased venous return had opposite effects. Changes in left ventricular function caused by changes in venous return alone were similar to those during mechanical ventilation except for minor quantitative differences. We conclude that phasic changes in systemic venous return during mechanical ventilation modulate left ventricular function by direct ventricular interaction.

Abdomen↗
PubMed2005

Ventricular interaction during mechanical ventilation in closed-chest anesthetized dogs.

The cardiac effects of positive pressure ventilation and positive end-expiratory pressure are incompletely understood. External constraint due to increased intrathoracic pressure decreases left ventricular end-diastolic volume; the effects on venous return and ventricular interaction are less clear. Phasic changes in inferior vena caval flow, end-diastolic ventricular dimensions and output were measured in seven anesthetized, ventilated normal dogs. During inspiration, caval flow, right ventricular diameter and output decreased; end-diastolic transseptal pressure gradient, septum-to-left ventricular free wall diameter, left ventricular area (ie, left ventricular volume index) and output increased despite the decreased sum of the septum-to-free wall diameters. The reverse occurred during expiration. Increased positive end-expiratory pressure decreased the left ventricular area, but the end-expiratory right ventricular diameter was unchanged. At given airway pressures, right ventricular diameter was greater at higher positive end-expiratory pressures, suggesting that a leftward septal shift (direct ventricular interaction) added to the effect of external constraint on left ventricular end-diastolic volume. In conclusion, positive pressure ventilation reduced right ventricular end-diastolic volume during inspiration and increased the transseptal pressure gradient, which shifted the septum rightward, increasing left ventricular end-diastolic volume and output. The reverse occurred during expiration. Positive end-expiratory pressure constrained left ventricular filling and decreased left ventricular end-diastolic volume further by a leftward septal shift.

Anesthesia↗
PubMed2004

Clinical usefulness of home oximetry compared with polysomnography for assessment of sleep apnea.

The practical purpose of diagnostic assessment in most cases of obstructive sleep apnea is to predict which patients have symptoms that will improve on treatment. We measured the accuracy with which clinicians make this prediction using polysomnography compared with oximeter-based home monitoring. Patients referred to a sleep center with suspicion of symptomatic obstructive sleep apnea were randomized to have polysomnography or home monitoring. Patients with comorbidity or physiologic consequences of sleep apnea were excluded. Sleep specialists estimated the likelihood of success of treatment as greater than 50% (predicted success) or less than 50% (predicted failure) on the basis of clinical data and test results. All patients were treated for 4 weeks with autoadjusting continuous positive airway pressure. Success was defined as an increase greater than 1.0 in Sleep Apnea Quality of Life Index. Correct prediction rates were compared. Two hundred eighty-eight patients were enrolled. Initial patient characteristics, compliance, and improvement in quality of life at 4 weeks were not different in the two groups. The correct prediction rate was 0.61 with polysomnography and 0.64 with home monitoring (not significant). We conclude that the ability of physicians to predict the outcome of continuous positive airway treatment in individual patients is not significantly better with polysomnography than with home oximeter-based monitoring.

Continuous Positive Airway Pressure↗
PubMedDate not supplied

Differences between middle cerebral artery blood velocity waveforms of young and postmenopausal women.

OBJECTIVE: We characterized middle cerebral artery (MCA) blood flow velocity waveforms measured by transcranial Doppler ultrasonography in premenopausal (26.6 +/- 6.1 years, mean +/- SD) and postmenopausal (54.0 +/- 3.6 years) women, of whom six were receiving hormone therapy (PM-HT) and seven were not (PM-non-HT). We hypothesized that feature points on MCA waveforms are altered in postmenopausal women compared with those in young women. DESIGN: A short protocol involved maintaining end-tidal PO2 at euoxia (88 mm Hg) and end-tidal PCO2 at 1.5 mm Hg above eucapnic values using a dynamic end-tidal forcing system. Doppler data for the velocity spectral outline (Vp) were collected every 10 ms, and velocity waveform analyses were done on a beat-by-beat basis. Waveform features were identified over each cardiac cycle, including the average Vp (VCYC), maximum acceleration (AMAX), and the ratio of the velocity at the reflected wave and the velocity at peak systole (VR:VMAX). RESULTS: VCYC was unchanged between premenopausal and postmenopausal women (69.4 +/- 9.6 and 67.5 +/- 11.1 cm/s, respectively). AMAX was significantly higher (P = 0.007) in premenopausal women (987.9 +/- 280.7 cm/s) compared with postmenopausal women (743.1 +/- 100.3). Conversely, VR:VMAX was significantly smaller (P < 0.001) in premenopausal women (0.90 +/- 0.09) compared with postmenopausal women (1.11 +/- 0.05). In postmenopausal women, the reflected wave is higher than the maximum velocity at peak systole, suggesting the presence of a shoulder in the MCA waveform. CONCLUSIONS: Further investigations are required to assess whether this waveform analysis can provide insight into pathophysiologic changes in cerebral hemodynamics with aging.

Adult↗