We measured phase and amplitude of compensated breath sounds (Ib/Tn), which are indexes of regional ventilation, with two microphones placed near the apex and base 10 cm apart on the chest wall, lateral to the right anterior axillary line in four seated normal subjects. We compared phase and amplitude of Ib/Tn with phase and amplitude of esophageal pressure changes (Pes) measured by two balloons positioned 10 cm apart and at approximately the same horizontal levels as the microphones. When breathing tidally below closing volume (CV), apical Ib/Tn was louder and earlier than basal Ib/Tn, whereas basal Pes was greater and earlier than apical Pes. Above CV basal Ib/Tn was louder than apical and the phase differences either disappeared or followed phase differences in PES. The results suggest that below CV, ventilation of lower zones lags behind upper ones probably due to airway closure. Pes measurements indicate that this may lead to an amplification of pleural pressure swings at the base. Above CV, all airways are open, the ventilation of lower zones is greater than that of upper zones, and the sequence of ventilation follows the sequence of pleural pressure changes.
OBJECTIVE: To examine the validity of self-reported information on obesity and high blood pressure (HBP) in relation to gender and age, and to explore the impacts of their misclassi®cation on the association between obesity and HBP. DESIGN: Community based cross-sectional study. SUBJECTS: 1791 adult subjects living in Humboldt, Saskatchewan, Canada. MEASUREMENTS: Objectively measured HBP was positive if systolic blood pressure (BP) was !140 mm Hg, diastolic BP was !90 mm Hg or the subject was currently using antihypertensive medication. Self-reported HBP was positive if the subjects gave an af®rmative response to the question:`Has a doctor ever said you had high blood pressure?' Body mass index (BMI) was calculated as weight (kg)aheight (m) 2 . Obesity was de®ned as a BMI b 27 kgam 2 . Measured obesity and reported obesity were based on measured and self-reported information on height and weight, respectively. RESULTS: The sensitivity of self-reported HBP was low, and was lower for men than for women, and for younger subjects than for older subjects. The speci®city was similar for both genders. Obese individuals had higher sensitivity and lower speci®city than non-obese individuals. The differential misclassi®cation of self-reported HBP caused a bias away from the null when the relative risk for HBP in relation to obesity was estimated. CONCLUSIONS: As a result of the gender-and age-related misclassi®cation of self-reported HBP, the modi®cation role of gender and age on the association between obesity and HBP could be altered. The bias caused by self-reported obesity was relatively small and was either toward or away from the null.
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