Time relative to NIPPV start (months) | Per cent total decline | FVCP in overall cohort | Change in FVCP/month in overall cohort | Change in FVCP/month (adherent) | Change in FVCP/month (nonadherent) |

∼30 | 0 | 74.0 | 0 | 0 | 0 |

b_{3}−b_{4} | 27 | 65.0 | −2.11 | −2.64 | −1.85 |

b_{3} | 50 | 57.3 | −2.69 | −3.35 | −2.35 |

b_{3}+b_{4} | 73 | 49.6 | −2.11 | −2.64 | −1.85 |

0 | ≥85 | 45.9 | −1.43 | −1.50 | −1.17 |

∼20 | 100 | 40.6 | 0 | 0 | 0 |

*b*_{3}: time (months) to the midpoint between the two asymptotes, also representing the inflection point of the FVCP time-course curve; *b*_{4}: a timescale factor (months) that reflects the rapidity of decline of forced vital capacity, such that a smaller *b*_{4} reflects a more rapid decline.

Slopes are derived from the first derivative of vital capacity with time of the following equation: FVCP = *b*_{1} + *b*_{2}/(1+e^{((b3}^{−t)/b4}^{)}) such that .