A description of sleep behaviour in healthy late pregnancy, and the accuracy of self-reports.

BACKGROUND: The importance of maternal sleep and its contribution to maternal and fetal health during pregnancy is increasingly being recognised. However, the ability to accurately recall sleep practices during pregnancy has been questioned. The aim of this study is to test the accuracy of recall of normal sleep practices in late pregnancy. METHODS: Thirty healthy women between 35 and 38 weeks of gestation underwent level III respiratory polysomnography (PSG) with infrared digital video recordings in their own homes. Data regarding sleep positions, number of times getting out of bed during the night and respiratory measures were collected. A sleep questionnaire was administered the morning after the recorded sleep. Continuous data were assessed using Spearman's Rho and Bland-Altman. Cohen's Kappa was used to assess recall in the categorical variables. RESULTS: Two-thirds of participants went to sleep on their left side. There was good agreement in sleep onset position between video and questionnaire data (Kappa 0.52), however the there was poor agreement on position on wakening (Kappa 0.24). The number of times getting out of bed during the night was accurately recalled (Kappa 0.65). Twenty five out of 30 participants snored as recorded by PSG. Questionnaire data was inaccurate for this measure. Bland-Altman plots demonstrated acceptable agreement between video and questionnaire data for estimated sleep duration, but not the time taken to fall asleep (sleep latency). One participant had mild obstructive sleep apnoea and another probable high upper airways resistance. CONCLUSIONS: Sleep onset position, sleep duration and the number of times getting out of bed during the night were accurately recalled, but sleep latency and sleep position on waking were not. This study identifies the sleep variables that can be accurately obtained by questionnaire and those that cannot.

Validation of thoracic impedance cardiography by echocardiography in healthy late pregnancy.

BACKGROUND: Assessment of stroke volume (SV) is often necessary in clinical and research settings. The clinically established method for SV assessment in pregnancy is echocardiography, but given its limitations, it is not always an appropriate measurement tool. Thoracic impedance cardiography (ICG) allows continuous, non-invasive SV assessment. However, SV determination relies on assumptions regarding the thoracic shape that may mean the algorithm is not valid in pregnancy. The available data regarding the validity of ICG against an established reference standard using modern SV algorithms are both limited and conflicting. We aimed to test the validity of ICG in a clinically realistic setting in late pregnancy using echocardiography. METHODS: Twenty-nine women in late pregnancy underwent standard echocardiography assessments with simultaneous ICG measurement. Agreement between devices was tested using Bland-Altman analysis. RESULTS: Bland-Altman analysis of the relationship between ICG and echocardiography demonstrated that the 95% limits of agreement exceeded acceptable or expected ranges. Measures of maternal and fetal anthropometry do not account for the lack of agreement. CONCLUSIONS: Absolute values of SV as determined by ICG are not valid in pregnancy. Further work is required to examine the ability of ICG to assess relative changes in maternal haemodynamics in late pregnancy.

Effect of surfactant deficiency and surfactant replacement on airway patency in the piglet lung.

We investigated the effect of surfactant deficiency on airway patency and the effectiveness of surfactant replacement as either an instilled liquid bolus, a non-hygroscopic aerosol or a hygroscopic aerosol. Small airway patency was assessed in isolated piglet lungs by passing a continuous flow of gas though a cannulated airway. Occlusion was assessed by measuring increases in pressure in the cannula that resulted from airway obstruction. In surfactant-deficient conditions the amount of airway closure increased approximately three-fold. However, administration of exogenous surfactant as an instilled liquid bolus, non-hygroscopic aerosol or a hygroscopic aerosol decreased airway closure such that it was statistically similar to that recorded prior to induction of surfactant deficiency, although the instilled and hygroscopic aerosol surfactant both appeared superior to the non-hygroscopic aerosol. These experiments showed that pulmonary surfactant does have a role in maintaining airway patency and that airway closure induced by surfactant deficiency could be reduced by administration of surfactant in any of the aforementioned forms.