The original formulation by Bohr, required measurement of the alveolar partial pressure P A. The Bohr equation is used to quantify the ratio of physiological dead space to the total tidal volume, and gives an indication of the extent of wasted ventilation. It differs from anatomical dead space as measured by Fowler's method as it includes alveolar dead space. This is given as a ratio of dead space to tidal volume. The Bohr equation, named after Danish physician Christian Bohr (1855–1911), describes the amount of physiological dead space in a person's lungs. Through measuring V(D) and V(D)/V(T) important information about lung ventilation can be obtained and the SBT is an easy method to use for this purpose.Not to be confused with the Bohr model or the Bohr effect. The single breath test (SBT) can be used for clinical evaluation of V(D) and V(D)/V(T) in anaesthetized ventilated dogs. The ICC revealed an excellent consistency for both methods. Linear regression analysis revealed a correlation coefficient (r(2)) of 0.79, 0.94, and 0.83 for PēCO(2), V(D) and V(D)/V(T), respectively. Intra-class correlation coefficient (ICC) was used to measure consistency of each method.įour measurement pairs were obtained in all 20 dogs for method SBT and MC. Method MC and SBT were compared using Bland-Altman plots and linear regression. Physiologic dead space variables (V(D) and V(D)/V(T)) were calculated manually (method MC) or automatically (method SBT) using the Bohr-Enghoff equation. At four time points arterial partial pressure of CO(2) (PaCO(2)) was measured.

Mixed expired CO(2) partial pressure (PēCO(2)) was measured by two methods: method MC by analysis, using an infrared capnograph, of the expired gas collected in a mixing box and method SBT which calculated it automatically by a device consisting of a mainstream capnograph and a pneumotachograph.

Twenty client-owned dogs, ASA I and II undergoing anaesthesia for clinical purposes.įollowing pre-medication, induction of anaesthesia, and intubation of the trachea, intermittent positive pressure ventilation was commenced. To compare physiologic dead space (V(D)) and physiologic dead space to tidal volume (V(T)) ratio (V(D)/V(T)) obtained by an automated single breath test for carbon dioxide (CO(2)) (method SBT) and a manual calculation (method MC) in ventilated healthy dogs.

What is physiologic dead space