Respiratory inductance plethysmography (RIP) is used to measure ventilation from two measurements of body surface movements (rib-cage and abdomen) via the application of volume-motion (V-M) coefficients. The correct derivation of both V-M coefficients (calibration) is necessary because there are considerable spontaneous variations in relative contributions from these two compartments even during resting breathing. In order to fully test a calibration, deliberate changes in rib-cage (RC) to abdominal (AB) contribution must be made. We used this approach to test two single-posture calibration techniques, multiple linear regression (MLR) and isovolume (ISV). Ten normal subjects and nine patients with chronic airway obstruction (CAWO) were studied using quiet breathing throughout. We also studied the effects of changing posture on the constancy of the V-M coefficients. MLR proved a little more accurate (p = 0.03) in deriving the V-M coefficients than ISV in normal subjects, and ISV consistently underestimated the AB V-M coefficient relative to RC. No difference between the two techniques existed in patients with CAWO. Both MLR and ISV calibrations failed to give acceptable calibrations in some patients. When MLR calibration was used, a deliberate 20% change in relative compartmental contribution (RC-AB) induced mean errors in RIP estimations of tidal volume of 3.5 and 9.5% in normal subjects and patients respectively. When there were no deliberate changes in relative contribution, the 95% confidence limits of individual tidal volume estimates were +/- 6.6 and +/- 12% in normal subjects and patients respectively. MLR calibration provides a statistical estimate of its quality at the time of V-M coefficient derivation.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMedDate not supplied

Speed of response and accuracy of two transcutaneous carbon dioxide monitors.

Two instruments (Radiometer and Hewlett-Packard) for measuring transcutaneous carbon dioxide levels have been compared. Their warm-up times, speed of response and accuracy in predicting arterial PCO2 have been assessed in six normal subjects and ten patients with respiratory problems. They both performed well with similar accuracy in predicting PaCO2 [95% confidence limits +/- 0.9 kPa (6.7 mmHg)]. The warm-up time following application depended on actual PaCO2, but was approximately 10 min for normal subjects and 15 min in patients. Their response to step changes in PaCO2 was complete in approximately 6 min. Prior skin abrasion (essential for the Hewlett-Packard) increased the speed of response of the Radiometer considerably and this is the faster instrument. The Hewlett-Packard proved easier to use. These instruments are a significant advance in non-invasive monitoring.

Adolescent↗

PubMedDate not supplied

The accuracy of the Hewlett-Packard 47201A ear oximeter below 50% saturation.

The Hewlett-Packard 47201A ear oximeter has been shown to measure arterial oxygen saturation (SaO2) above 50% SaO2 with an accuracy of +/- 5%. Below 50% SaO2, the oximeter underestimates arterial saturation in a predictable way, thus allowing a correction factor to be used: true SaO2 = (oximeter reading + 50)/2.

Blood Gas Analysis↗

PubMedDate not supplied

Sleep apnoea: clinical importance and facilities for investigation and treatment in the UK. Addendum to the 1993 Royal College of Physicians Sleep Apnoea report.

The potential importance of the obstructive sleep apnoea syndrome (OSA) has been recognized only in the last few years. Epidemiological studies suggest that symptomatic OSA occurs in 1-2% of middle-aged men and in approximately half that number of women. The relation of OSA to vascular disease is uncertain and the main indication for treatment is the relief of disabling sleepiness. Two recent evidence based analyses have produced diametrically opposed conclusions on the efficacy of treatment with nasal continuous positive airway pressure (CPAP). However, recent controlled studies confirm the overwhelming clinical experience of benefit. Facilities for the investigation and treatment of patients with OSA in the UK are subject to severe financial constraints and the availability of CPAP treatment lags markedly behind that in other countries for which data are available.

Age Distribution↗