Sigmoidal equation for lung and chest wall volume-pressure curves in acute respiratory failure

Abstract

To assess incidence and magnitude of the "lower inflection point" of the chest wall, the sigmoidal equation was used in 36 consecutive patients intubated and mechanically ventilated with acute lung injury (ALI). They were 21 primary and 5 secondary ALI, 6 unilateral pneumonia, and 4 cardiogenic pulmonary edema. The lower inflection point was estimated as the point of maximal compliance increase. The low constant flow inflation method and esophageal pressure were used to partition the volume-pressure curves into their chest wall and lung components on zero end-expiratory pressure. The sigmoidal equation had an excellent fit with coefficients of determination >0.90 in all instances. The point of maximal compliance increase of the chest wall ranged from 0 to 8.3 cmH2O (median 1 cmH2O) with no difference between ALI groups. The chest wall significantly contributed to the lower inflection point of the respiratory system in eight patients only. The occurrence of a significant contribution of the chest wall to the lower inflection point of the respiratory system is lower than anticipated. The sigmoidal equation is able to determine precisely the point of the maximal compliance increase of lung and chest wall.

The physical origin of sigmoidal respiratory pressure–volume curves: Alveolar recruitment and nonlinear elasticity

“…Using our theory, we can interpret the sigmoidal anti-symmetry of respiratory P-V curves indicated by various experiments [3,[10][11][12][13][14][15][16][17]. Any inflation is anti-symmetrical with respect to (V tlc + V min ) /2.…”

“…It is remarkably good in the description of the P-V curves of the lungs and of the chest wall [11]. Here, we insert the unifying idea that the sigmoidal shape has its origin in the lung, resulting exclusively from the recruitment mechanism occurring in this organ [26][27][28][29][30].…”

“…(1) to experimental data from patients with acute respiratory distress syndrome (ARDS), and acute lung injury (ALI) [3,[10][11][12][13], or to data from animal models [14][15][16][17]. The main features of a general respiratory P-V curve determined from such fits are its asymptotic volumes V max and V min , as well as the parameters P i,d , and κ i,d , which have dimensions of force per unit area.…”

Recent advances in theoretical models of respiratory mechanics

“…is helpful when using ventilators [10]. Recently, Schumann et al [11] used a gliding-SLICE method to fit P-V curves, which is able to evaluate the local continuous nonlinear compliance of the lungs.…”

“…1 Schematic drawing of typical respiratory mechanics models. a The respiratory system and blood circulation system, in which the arrows and circles show the position concerned with the corresponding model (RA, right atrium; RV, right ventricle; LA, left atrium; LV, left ventricle); b A macroscopic model that merely considers the oxygen consumption and carbon dioxide production of a mobile human body in a chamber; c A typical inflation P-V curve in a patient with ARDS, including the parameters in a sigmoidal model [10]; d A generated 1D centerline airway tree containing the 3D CT-resolved upper airway, central airway tree, and central airway skeleton [20]; e A two-compartment lumped parameter model, in which the spring and dashpot represent the static elasticity and the resistance, and a module comprising a dashpot and a spring reflect the tissue viscoelasticity [14]; f A model showing the process of oxygen uptake of blood flowing through the pulmonary capillaries [29]; g A lung-heart coupling model that includes gas exchange between alveolar gas and blood, as well as blood gas transport [40] the heart was thus investigated [41,42]. One recent study combined a ventilatory neuromuscular model and a cardiovascular model [43].…”