A neoprene vest hastens dyspnoea and leg fatigue during exercise testing: entangled breathing and cardiac hindrance?

Symptoms and contributing factors of immersion pulmonary oedema (IPO) are not observed during non-immersed heart and lung function assessments. We report a case in which intense snorkelling led to IPO, which was subsequently investigated by duplicating cardiopulmonary exercise testing with (neoprene vest test – NVT) and without (standard test – ST) the wearing of a neoprene vest. The two trials utilised the same incremental cycling exercise protocol. The vest hastened the occurrence and intensity of dyspnoea and leg fatigue (Borg scales) and led to an earlier interruption of effort. Minute ventilation and breathing frequency rose faster in the NVT, while systolic blood pressure and pulse pressure were lower than in the ST. These observations suggest that restrictive loading of inspiratory work caused a faster rise of intensity and unpleasant sensations while possibly promoting pulmonary congestion, heart filling impairment and lowering blood flow to the exercising muscles. The subject reported sensations close to those of the immersed event in the NVT. These observations may indicate that increased external inspiratory loading imposed by a tight vest during immersion could contribute to pathophysiological events.

Calculating the work of breathing during mechanical ventilation.

Left figure: Passive patient esophageal pressure (Pes) in cmH2O on x-axis versus tidal volume in ml on y-axis. Green dashed line represents the chest wall compliance Right figure: same patient actively breathing on pressure support ventilation. (Pes) in cmH2O on x-axis versus tidal volume in ml on y-axis. Green dashed line represents the chest wall compliance. Red shaded area is the Campbell diagram representing the inspiratory work of breathing

Performance and work of nasal breathing

OBJECTIVE. To evaluate performance (Q) and work (W) of nasal breathing as potential parameters in functional diagnostic of nasal obstruction. MATERIAL AND METHODS. We included in our study 250 patients and we measured by 4-phase-rhinomanometry with decongestion test. We calculated performance Q of the “representative breath” in inspiration and expiration and in total breath, maximal performance Q (Qmax), Work W of nasal breathing in mJ and in mJ/litre and Q in J/min. RESULTS. The interquartile range of Win for representative breath before decongestion is 356 mJ/l, Wex 308 mJ/l, while after decongestion Win is 264 mJ/l and Wex 220 mJ/l. There is no significant difference between work before and after decongestion (p<0.001). Interquartile range for nasal breathing Q before decongestion is 19.2 J/min and after – 14.3 J/min. A significant correlation exists between logarithmic vertex resistance for inspiration and expiration and Qmax for inspiration and expiration (p<0.001). That means that the performance required by breathing depends in the first line on nasal resistance. CONCLUSION. Inspiratory work is 1.2 times higher than expiration work. Increase in nasal airway resistance is followed by increase in maximal nasal performance.

Effect of changing the gravity vector on respiratory output and control

We studied the respiratory output in five subjects exposed to parabolic flights [gravity vector 1, 1.8 and 0 gravity vector in the craniocaudal direction (Gz)] and when switching from sitting to supine (legs bent at the knees). Despite differences in total respiratory compliance (highest at 0 Gz and in supine and minimum at 1.8 Gz), no significant changes in elastic inspiratory work were observed in the various conditions, except when comparing 1.8 Gz with 1 Gz (subjects were in the seated position in all circumstances), although the elastic work had an inverse relationship with total respiratory compliance that was highest at 0 Gz and in supine posture and minimum at 1.8 Gz. Relative to 1 Gz, lung resistance (airways plus lung tissue) increased significantly by 52% in the supine but slightly decreased at 0 Gz. We calculated, for each condition, the tidal volume changes based on the energy available in the preceding phase and concluded that an increase in inspiratory muscle output occurs when respiratory load increases (e.g., going from 0 to 1.8 Gz), whereas a decrease occurs in the opposite case (e.g., from 1.8 to 0 Gz). Despite these immediate changes, ventilation increased, going to 1.8 and 0 Gz (up to ≈23%), reflecting an increase in mean inspiratory flow rate, tidal volume, and respiratory frequency, while ventilation decreased (approximately −14%), shifting to supine posture (transition time ∼15 s). These data suggest a remarkable feature in the mechanical arrangement of the respiratory system such that it can maintain the ventilatory output with small changes in inspiratory muscle work in face of considerable changes in configuration and mechanical properties.