274
A. Colantuoni and D. Lapi
17.1 Historical Background
Oscillations in vessel diameter were reported as early as 1852 by Jones in the bat
wing, where rhythmic contractions of venular vessels with fast frequency (more than
20 cycles per min, cpm) were described [27]. However, we had to wait until the new
century, when Krogh introduced the concept of capillary recruitment in [16, 17], due
to precapillary sphincters, and Clark and Clark [6] described in an in vivo preparation
(rabbit ear chamber) calibre changes in minute vessels. They observed constriction
and dilation of arterioles with a frequency in the range 2–3 cpm.
Chambers and Zweifach [5] reported oscillations in capillary blood flow, but
the fundamental finding was the organization of the microcirculation around the
metarteriole in the mesentery of frog and other experimental models. Nicoll and Webb
[23] for the first time defined vasomotion as the outstanding motor phenomenon in the
vasculature. They reported the rhythmic changes in diameter of venules and arterioles
describing the microcirculation in the bat wing. However, the effects of arteriolar
diameter changes on vascular tone were highlighted by Folkow [14], who suggested
that many points in the arterial circulation endowed with peripheral pacemakers are
able to regulate vascular tone through contraction of vascular smooth muscle cells.
Wiederhielm and Weston [26] reported irregular vasomotion in small arteries
and arterioles, but regular activity in metarterioles and precapillary sphincters in
the same model of bat wing. Further data on vasomotion or changes in blood flow
were presented in the 70’s and 80’s of the last century in rabbit tenuissimus muscle
[21], isolated sartorius muscle [25], isolated arterioles of the hamster cheek pouch
[12], cremaster muscle of decerebrate rat [13]. Therefore, arteriolar vasomotion was
detected in different tissues, while isolated arterioles were able to constrict and dilate:
all data indicated that rhythmic changes in arteriolar diameter occur with and without
anesthesia, characterized by frequencies quite in the same ranges.
17.2 Vasomotion in Hamster Dorsal Skin Fold Window
Preparation
In the laboratory of Marcos Intaglietta we implemented the dorsal skin fold chamber
window preparation to observe microcirculation in hamsters without anesthesia and
acute surgical trauma [7, 8]. We defined the pattern of arteriolar rhythmic diameter changes along the arteriolar networks in subcutaneous tissue, while we did not
detect diameter changes in venular vessels. It was of interest that branching points
were present in discrete points of the arteriolar networks and from these branching
points originated oscillations in vessel diameter which were effective in producing
oscillations in blood flow in downstream vessels right down to the capillaries. The
amplitude of these diameter changes was different according to arteriolar diameter:
from the largest arterioles (15–30% of mean diameter) down to the smallest ones
(85–100% of mean diameter). The frequencies of these oscillations were inversely
A. Colantuoni and D. Lapi
17.1 Historical Background
Oscillations in vessel diameter were reported as early as 1852 by Jones in the bat
wing, where rhythmic contractions of venular vessels with fast frequency (more than
20 cycles per min, cpm) were described [27]. However, we had to wait until the new
century, when Krogh introduced the concept of capillary recruitment in [16, 17], due
to precapillary sphincters, and Clark and Clark [6] described in an in vivo preparation
(rabbit ear chamber) calibre changes in minute vessels. They observed constriction
and dilation of arterioles with a frequency in the range 2–3 cpm.
Chambers and Zweifach [5] reported oscillations in capillary blood flow, but
the fundamental finding was the organization of the microcirculation around the
metarteriole in the mesentery of frog and other experimental models. Nicoll and Webb
[23] for the first time defined vasomotion as the outstanding motor phenomenon in the
vasculature. They reported the rhythmic changes in diameter of venules and arterioles
describing the microcirculation in the bat wing. However, the effects of arteriolar
diameter changes on vascular tone were highlighted by Folkow [14], who suggested
that many points in the arterial circulation endowed with peripheral pacemakers are
able to regulate vascular tone through contraction of vascular smooth muscle cells.
Wiederhielm and Weston [26] reported irregular vasomotion in small arteries
and arterioles, but regular activity in metarterioles and precapillary sphincters in
the same model of bat wing. Further data on vasomotion or changes in blood flow
were presented in the 70’s and 80’s of the last century in rabbit tenuissimus muscle
[21], isolated sartorius muscle [25], isolated arterioles of the hamster cheek pouch
[12], cremaster muscle of decerebrate rat [13]. Therefore, arteriolar vasomotion was
detected in different tissues, while isolated arterioles were able to constrict and dilate:
all data indicated that rhythmic changes in arteriolar diameter occur with and without
anesthesia, characterized by frequencies quite in the same ranges.
17.2 Vasomotion in Hamster Dorsal Skin Fold Window
Preparation
In the laboratory of Marcos Intaglietta we implemented the dorsal skin fold chamber
window preparation to observe microcirculation in hamsters without anesthesia and
acute surgical trauma [7, 8]. We defined the pattern of arteriolar rhythmic diameter changes along the arteriolar networks in subcutaneous tissue, while we did not
detect diameter changes in venular vessels. It was of interest that branching points
were present in discrete points of the arteriolar networks and from these branching
points originated oscillations in vessel diameter which were effective in producing
oscillations in blood flow in downstream vessels right down to the capillaries. The
amplitude of these diameter changes was different according to arteriolar diameter:
from the largest arterioles (15–30% of mean diameter) down to the smallest ones
(85–100% of mean diameter). The frequencies of these oscillations were inversely