High-frequency electrical stimulation of cervical vagi reduces airway response to methacholine

Figure 1 Typical total lung resistance and dynamic pulmonary compliance responses to electrical stimulations in an Ova-sensitized guinea pig. The traces from the top to bottom are arterial blood pressure (ABP), airflow (Flow), Trans-pulmonary pressure (P_tp), total lung resistance (R_L) and dynamic pulmonary compliance (C_dyn). The dashed lines in each column reflect the on- and off-set of a given electrical stimulation. Vagal electrical stimulation included low-frequency electrical stimulation (LES, monophasic stimulation at 50 Hz); HESb1 and HESb2 (biphasic waveform at 1 and 2.5 kHz); and HESm1 and HESm2 (monophasic waveform at 1 kHz and 2.5 kHz), which are the same for the following figures.

Figure 2 Group data showing the responses to vagal electrical stimulations. MABP: Mean arterial blood pressure; HR: Heart rate; R_L: Total lung resistance; C_dyn: Dynamic pulmonary compliance. n = 9 and 8 in the Sal- and Ova-pretreated guinea pigs; Mean ± SE. ^bP < 0.01, vs the data immediately before electrical stimulation presented as “0”; ^dP < 0.01, low-frequency electrical stimulation (LES) vs high-frequency electrical stimulations (HESs).

Figure 3 Typical examples exhibiting cardiovascular and airway responses to methacholine aerosol (100 μg/mL per minute for 2 min) and to vagal electrical stimulation in an anesthetized and paralyzed Ova-pretreated guinea pig. The traces from the top to bottom are arterial blood pressure (ABP), heart rate (HR), total lung resistance (R_L) and dynamic pulmonary compliance (C_dyn). The duration of the break is about 1 min. MCh: Methacholine. HES: High-frequency electrical stimulation.

Figure 4 Peak airway responses to methacholine aerosol (100 μg/mL per minute for 2 min) and the associated cardiovascular changes. n = 9 and 8 in Sal- and Ova-treated guinea pigs respectively; mean ± SE. ^bP < 0.01, vs the data of pre-methacholine (MCh) challenge presented as “0”; ^dP < 0.01 between Sal- and Ova-treated groups. MABP: Mean arterial blood pressure; HR: Heart rate; R_L: Total lung resistance; C_dyn: Dynamic pulmonary compliance.

Figure 5 Airway and cardiovascular responses to the vagal electrical stimulations after exposure to methacholine aerosal (100 μg/mL per minute for 2 min). n = 8 and 9 in Sal- and Ova-treated guinea pigs; Mean ± SE. ^bP < 0.01, compared to the data before methacholine (MCh) challenge; ^dP < 0.01 LES vs HESs; ^fP < 0.01 between Sal- and Ova-treated groups. MABP: Mean arterial blood pressure; HR: Heart rate; R_L: Total lung resistance; C_dyn: Dynamic pulmonary compliance.

Figure 6 Cardiovascular and airway responses to 2 min vagal high-frequency electrical stimulation after exposure to methacholine aerosal (100 μg/mL per minute for 2 min). A: HESm1-evoked responses in an Ova-treated guinea pig about 2 min after initiation of methacholine (MCh) challenge, in which the baseline values of total lung resistance (R_L) and dynamic pulmonary compliance (C_dyn) were 0.1 cmH₂O s/mL and 0.4 mL/cmH₂O respectively; B: The averaged data of MABP, HR, R_L and C_dyn from three guinea pigs (five trials) are illustrated in panel. In both panels, the traces are arterial blood pressure (ABP/MABP), heart rate (HR), R_L, and C_dyn. n = 5 trials (3 guinea pigs); Mean ± SE; ^aP < 0.05, high-frequency electrical stimulation (HES)-evoked responses vs the data before electrical stimulation presented as “0”.

Figure 7 Comparison of the cardiovascular and airway responses to methacholine aerosol (100 μg/mL per minute for 2 min) before and after bivagotomy in an anesthetized and paralyzed Ova-treated guinea pig. The traces are arterial blood pressure (ABP), heart rate (HR), total lung resistance (R_L), and dynamic pulmonary compliance (C_dyn).