The ventilatory response to carbon dioxide. An analysis of data obtained by the rebreathing method

The ventilatory response to carbon dioxide using the rebreathing method was studied repeatedly in four healthy volunteers. The data were collected and processed in different ways using a microcomputer. Least squares linear regression analysis described the responses almost as accurately as a non-linear second-order polynomial regression. Linear regression analysis was undertaken on VI/PE'CO2 points, first breath-by-breath and then on three different groupings of breaths. The gradients and intercepts obtained by grouping agreed with those from breath-by-breath analysis both for a single response and for the mean result of a number of responses. Grouping tended to increase the correlation coefficient of a response, but widened the statistical confidence limits of the calculated gradient. The performance variability between repeated responses, the same no matter which data points were used, produced a range of gradients for each subject which was larger than the confidence limits on the gradient of a single response.