Non‐invasive prospective targeting of arterial <i>P</i> in subjects at rest

Accurate measurements of arterial P (P) currently require blood sampling because the end‐tidal P (P) of the expired gas often does not accurately reflect the mean alveolar P and P. Differences between P and P result from regional inhomogeneities in perfusion and gas exchange. We hypothesized that breathing via a sequential gas delivery circuit would reduce these inhomogeneities sufficiently to allow accurate prediction of P from P. We tested this hypothesis in five healthy middle‐aged men by comparing their P values with P values at various combinations of P (between 35 and 50 mmHg), P (between 70 and 300 mmHg), and breathing frequencies (f; between 6 and 24 breaths min−1). Once each individual was in a steady state, P was collected in duplicate by consecutive blood samples to assess its repeatability. The difference between P and average P was 0.5 ± 1.7 mmHg (P= 0.53; 95% CI −2.8, 3.8 mmHg) whereas the mean difference between the two measurements of P was −0.1 ± 1.6 mmHg (95% CI −3.7, 2.6 mmHg). Repeated measures ANOVAs revealed no significant differences between P and P over the ranges of P, f and target P. We conclude that when breathing via a sequential gas delivery circuit, P provides as accurate a measurement of P as the actual analysis of arterial blood.

Non‐invasive prospective targeting of arterial P in subjects at rest Journal Articles