Abstract: The invention provides an estimation of key flow-independent parameters characteristic of NO exchange in the lungs, namely: 1) the steady state alveolar concentration, Calv,ss; 2) the maximum flux of NO from the airways, JNO,max; and 3) the diffusing capacity of NO in the airways, DNO,air. The parameters were estimated from a single exhalation maneuver comprised of a pre-expiratory breathhold, followed by an exhalation in which the flow rate progressively decreased. The mean values for JNO,max, DNO,air, and Calv,ss do not depend on breathhold time for breathhold times greater than approximately 10 seconds. A priori estimates of the parameter confidence intervals demonstrates that a breathhold no longer than 20 seconds may be adequate, and that JNO,max be can estimated with the smallest uncertainty, and DNO,air the largest.