Changes in lung fluid levels with variations in the respiratory cycle

The association between respirophasic variation and lung fluid levels is unknown. Remote dielectric sensing (ReDS™) is a novel non-invasive technology to quantify lung fluid levels. We investigated the change in ReDS values over the course of the respiratory cycle. Patients with clinically stable chronic heart failure at outpatient clinics were prospectively included. ReDS values were measured at three respiratory statuses and compared: (1) at rest with normal breathing, (2) at inspiration, and (3) at expiration. A total of 11 patients were included. Median age was 73 (58, 78) years and 9 were men. ReDS value was 28% (25%, 32%) at rest and decreased significantly with inspiration down to 26% (24%, 30%) (p = 0.004). ReDS value were significantly higher on expiration as 30% (27%, 34%) as compared with rest (p = 0.003). Lung fluid levels in chronic heart failure patients can vary with changes in the respiratory cycle—attention should be paid to what point in the respiratory cycle measurements are taken when interpreting results in each modality, such as chest X-ray (measured at inspiratory status) and right heart catheterization (measured at expiratory status). ReDS system might be a physiologically ideal modality to assess lung fluid amount under natural breathing.