Try something like this:
wheezes = sort(randi(100, 10, 1)); % Create Data
wsnew = wheezes(1:2:end); % Create Data
wenew = wheezes(2:2:end); % Create Data
x = linspace(0, 100, 100);
breathsounds = rand(size(x));
figure
plot(x, breathsounds)
hold on
plot(x(wsnew*[1 1]).', (ones(size(wsnew,1),2).*ylim).', '-g', 'LineWidth',2)
plot(x(wenew*[1 1]).', (ones(size(wenew,1),2).*ylim).', '-r', 'LineWidth',2)
hold off
grid
.
