Expiratory flow limitation as a determinant of orthopnea in acute left heart failure
Alexandre Duguet, MD*,
Claudio Tantucci, MD*  ,
Olivier Lozinguez, MD ,
Richard Isnard, MD,
Daniel Thomas, MD,
Marc Zelter, MD ,
Jean-Philippe Derenne, MD*,
Joseph Milic-Emili, MD, PhD|| and
Thomas Similowski, MD, PhD*
* Laboratoire de Physiopathologie Respiratoire du Service de Pneumologie, Groupe Hospitalier Pitié-Salpêtrière, Paris, France
Service de Cardiologie , Groupe Hospitalier Pitié-Salpêtrière, Paris, France
Laboratoire Central d’Exploration Fonctionnelle Respiratoire, Groupe Hospitalier Pitié-Salpêtrière, Paris, France
Clinica di Semeiotica Medica, University of Ancona, Ancona, Italy
|| Meakins-Christie Laboratories, McGill University, Montréal, Québec, Canada
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Figure 1 Schematic representation of flow-volume curves in a normal subject (left) and in a patient with severe chronic obstructive pulmonary disease (COPD) (right). The outermost curves correspond to a forced maneuver, the innermost curves to tidal breathing. In the normal subject, the maximal expiratory envelope is way above the tidal one. In the COPD patient, maximal expiratory flows are reduced at all lung volumes and dramatically so at low lung volumes. Tidal expiratory flow reaches the maximal expiratory flow, defining flow limitation. As compared with normal subjects, residual volume (RV) and functional residual capacity (FRC) are shifted toward total lung capacity (TLC), defining hyperinflation: RV in the patient approximately corresponds to FRC in the normal subject. COPD = chronic obstructive pulmonary disease; FRC = functional residual capacity; TLC = total lung capacity; RV = residual volume.
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Figure 2 Schematic representation of the experimental setup used. A Venturi system is placed in series with a pneumotachograph and a mouthpiece, allowing measurement of flow, volume and mouth pressure (Pm), respectively. When compressed air is fed through the Venturi via a computer-driven valve, a negative pressure is generated at the mouth. Its value can be adjusted using a potentiometer. Signals are conditioned, monitored and stored on a personal computer. Volume is obtained by numerical integration of the flow signal. Pm = mouth pressure.
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Figure 3 Top panel: Flow (top trace), volume (middle trace) and mouth pressure (Pm, bottom trace) vs. time. Negative expiratory pressure (NEP) is applied during the last expiration shown (Pm trace). The ensuing expiratory flow is not different from that observed during the preceding control expiration, defining flow limitation (FL). Bottom panel: Examples of flow-volume curves in response to NEP (arrows) with corresponding curves of preceding control breaths. In the patient without FL (nFL, left), the expiratory flow-volume curve with NEP is above that of the control breathing cycle throughout expiration. In the patient with partial FL (pFL, middle), the expiratory flow-volume curve with NEP is superimposed on the latter part of the corresponding control expiratory flow-volume curve. In the patient with complete FL (cFL, right), the expiratory flow-volume curve with NEP is superimposed on the whole control curve, except for an initial transient increase in flow. See text for further details. cFL = completely flow limited; FRC = functional residual capacity; NEP = negative expiratory pressure; nFL = not flow limited; pFL = partially flow limited; Pm = mouth pressure.
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Figure 4 Average breathing cycle in the seated (solid lines) and the supine (dashed lines) position, in control subjects (left panel) and patients with acute left heart failure (right panel). Bars represent one standard deviation (maximal standard deviation noted in each group at each point). Between groups, differences are statistically significant, whereas between positions, they are not. E = expiration; I = inspiration.
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Figure 5 Effects of changing position on flow limitation (FL) and orthopnea. Each patient is represented by a number and a symbol placed in the compartment corresponding to his degree of FL. Closed symbols represent the patients reporting orthopnea, while open symbols correspond to patients without orthopnea. cFL = completely flow limited; nFL = not flow limited; pFL = partially flow limited.
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Figure 6 Time course of the effect of postural changes on the response to negative expiratory pressure (NEP). Four left panels, in a representative patient (#2); two right panels, in a control subject. In the patient when first studied seated, flow limitation (FL) encompasses less than 50% of tidal volume (pFL; top panel, left). Flow limitation worsens (more than 50% of tidal volume, cFL) in supine position (top panel, right) and diminishes when the patient returns to the sitting position (bottom panels). The degree of FL continues to decrease for several minutes after resuming the sitting position, and after 15 min, the patient is no longer flow limited. In the control subject, there is no FL.
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